feat(input): full controller support, rebindable controls, and rotation fixes

Playing with a gamepad did not work: all six move_* actions had no joypad
event at all, so a pad could yaw/pitch/roll/turbo but could not translate.
Nothing caught it because every action existed and the game booted fine —
no assertion checked that an action is reachable on *both* devices.

Controller layout, on the 6DOF convention (left stick aims, right stick
translates), using all six of the pad's analog axes for the ship's six
degrees of freedom:

  left stick   yaw + pitch        right stick  strafe + vertical
  LB / RB      roll               RT / LT      forward / back
  L3           turbo              R3           ball camera

Input is now read with Input.get_axis instead of is_action_pressed, so
triggers and sticks are proportional. Keyboard values are unchanged.

Three rotation bugs found by measuring a real Ship rather than reading the
code:

- apply_torque() is world-space and the torque was never rotated into the
  hull's frame (unlike thrust, which uses -ship_basis.z). Roll input became
  pitch after a 90 degree turn and inverted at 180, so the controls were
  correct flying up-field and backwards flying back.
- ship.tscn's inertia is Vector3(7, 1, 7) but a flat torque was applied to
  every axis, giving yaw 7x the angular acceleration of pitch and roll
  (172 deg/s vs 52). Torque is now scaled per-axis by inertia, so
  rotation_acceleration means rad/s^2 and all three axes match. Yaw is
  unchanged.
- pitch_down pitched the nose UP: get_axis's arguments were reversed, so
  the I/K keys and the stick each did the opposite of their label.

Menus were unusable on a pad for a separate reason: Godot 4.7 gives
ui_up/down/left/right joypad events by default but leaves ui_accept and
ui_cancel with none (verified against a pristine project), so a controller
could move the highlight and never press anything. A confirms and B goes
back. Gameplay exits on a new leave_gameplay action (Escape / Start) rather
than ui_cancel, so carrying B for menus cannot abandon a live match.

Bindings for both devices are rebindable in Settings -> Controls, persisted
to user://input.cfg — a separate file from settings.cfg because
VideoSettings.save() rewrites that file wholesale and would drop any
section it does not know about. project.godot stays the source of truth for
defaults; overrides are only ever a delta on top of a boot-time snapshot.

Verified: 268 unit tests, the ENet integration gate, and a 16-sample
before/after comparison of networked prediction residuals showing the
physics change does not regress them (median 0.083m -> 0.065m).

Note for follow-up: every policy in Game/bots/ was trained against the old
sluggish, world-axis rotation and will over-rotate until retrained.

FLIGHT_MANUAL.md

@@ -27,18 +27,58 @@ Welcome to space, pilot! This guide will teach you everything you need to know a
 
 ### Controller Controls
 
-#### Translation
+Button names are the Xbox layout; a PlayStation pad maps the same physical
+positions (A = ✕, B = ○, X = □, Y = △).
 
-- Left Stick - Strafe (Left/Right) + Thrust (Forward/Back)
-- Right Trigger - Forward Thrust
-- Left Trigger - Reverse Thrust
-- Face Buttons - Up/Down Thrust
+**The left stick points the nose, the right stick moves the hull.** Your ship has
+six degrees of freedom and a pad has exactly six analog axes, so every one gets a
+real axis rather than an on/off button.
 
-#### Rotation
+#### Rotation — left stick and shoulders
 
-- Right Stick - Pitch/Yaw
-- Shoulder Buttons - Roll
-- `A Button` - Turbo Boost
+- Left Stick (left/right) - Yaw
+- Left Stick (up/down) - Pitch. Flight-sim polarity by default: **push the
+  stick forward and the nose goes down.** Flip it with "Invert pitch" in
+  Settings → Controls.
+- `LB` - Roll Left (Bank Left)
+- `RB` - Roll Right (Bank Right)
+
+#### Translation — right stick and triggers
+
+- `RT` - Forward Thrust (Main Engines)
+- `LT` - Reverse Thrust (Retro Engines)
+- Right Stick (left/right) - Strafe (Port/Starboard Thrusters)
+- Right Stick (up/down) - Thrust Up/Down (Dorsal/Ventral Thrusters)
+- `L3` (click the left stick) - Turbo Boost
+
+`X` and `Y` are deliberately unused in flight, and `A`/`B` are menu-only, so a
+reflexive face-button press never does anything mid-match.
+
+#### Menus
+
+- D-Pad or Left Stick - move the highlight
+- `A` - select
+- `B` - back
+- `Start` - leave a match in progress (deliberately not `B`, which is too easy
+  to press by accident mid-game)
+
+#### Other
+
+- `R3` (click the right stick) - Toggle ball camera
+- `D-Pad Up` - Reset the ball (Free Play only)
+
+The triggers and sticks are **analog**: a half-pulled trigger gives half thrust,
+and a gentle stick lean gives a gentle turn. Keyboard keys are all-or-nothing,
+which is the main reason a pad is easier to fly precisely.
+
+### Rebinding
+
+Every control above — keyboard and controller alike — can be remapped in
+**Settings → Controls**. Pick the device with the Keyboard/Controller toggle,
+click the binding you want to change, and press the key or button to assign.
+Binding an input that is already in use unbinds it from the action that had it,
+and the screen tells you which. "Reset all bindings to defaults" restores this
+table.
 
 ## 🛸 Basic Flight Principles
 
@@ -69,7 +109,7 @@ Your ship is a **realistic space vehicle** with the following characteristics:
 
 #### Camera Control
 
-- **Ball Cam**: Press `Enter` to toggle ball tracking camera
+- **Ball Cam**: Press `Space` (or `R3` on a controller) to toggle ball tracking camera
 - **Ship Cam**: Normal follow camera that looks where your ship points
 
 ### Intermediate Maneuvers
@@ -115,7 +155,7 @@ Your ship is a **realistic space vehicle** with the following characteristics:
 
 ## 🎮 Ball Cam vs Ship Cam
 
-### Ball Cam Mode (`Enter` to toggle)
+### Ball Cam Mode (`Space` / `R3` to toggle)
 
 - **Camera**: Always looks toward the ball
 - **Ship Control**: Based on ship orientation (NOT camera view)
@@ -133,7 +173,7 @@ Your ship is a **realistic space vehicle** with the following characteristics:
 
 ### Turbo System
 
-- **Activation**: Hold `Shift` (keyboard) or `A` (controller) while thrusting forward
+- **Activation**: Hold `Shift` (keyboard) or `L3` (controller) while thrusting forward
 - **Effect**: 2.5x thrust multiplier on main engines only
 - **Strategy**: Use for quick acceleration or emergency maneuvers