D300: hipfire direct camera look (WI-1); D243 M-159/160/161 investigation

D300: new hipDirectCompute() in port/src/input.c writes vv_theta/vv_verta
directly for hipfire mouse-look, mirroring GEPD's linear px->degree model
and the existing D194 aim-mode pattern -- replaces the N64 stick-curve
routing that saturated at ~13 px/poll (issue #89). Ported GEPD's
dead/watch/pause safety gates. Input.MouseDirectLook=1 default, escape
hatch to the legacy path. User-confirmed better feel in a live playtest.

D243: added a permanent onscreen-visibility probe (D243M: onscreen,
chr.c) to test whether chrTick's posIsOnScreen gate explains the
abseil cutscene's frozen render position (M-159). A live capture
refuted that and found the real mechanism instead: chrTick overwrites
prop->pos with a stale value via its own chrUpdateAnim/modelTickAnim
animation-position logic, racing the AI script's scripted write
(M-160). A decisive throwaway experiment neutralizing that overwrite
produced no visible change in a live playtest (M-161) -- the mechanism
is real but isn't the dominant visible cause. Experiment reverted;
D243 parked pending a new lead after ~15 session-passes without a fix.

Docs: findings.md/findings-index.csv/porting-notes.md/GE-ENV-PROBES.md
updated throughout.

AGENTS.md

@@ -26,6 +26,7 @@
 | `port/src/` | Shims: `libultra.c` (OS API), `gesched.c` (scheduler), `n64stubs.c` (boot/TLB/FPU/rmon), `random.c` (PRNG ported verbatim from `random.s`), `ucode.c` (microcode segment markers), `main.c`, `video.c`, … |
 | `port/fast3d/` | Software RSP (adapted from the PD port). The main Phase 2 work. |
 | `rsp/graphics/gmain.s` | GE's RSP ucode — ground truth for GBI/CC/RM. |
+| `reference/mouse-injector/` | Vendored GEPD-Edition Mouse Injector source (GPLv2, read-only reference — never compile or modify). Ground truth for the mouse-aim model: `games/goldeneye.c` is the whole GE aim/hipfire/menu model (our D194 mirror); see its README + `docs/dev/GEPD-INPUT-PLAN.md`. |
 | A local **Perfect Dark PC port** checkout ([fgsfdsfgs/perfect_dark](https://github.com/fgsfdsfgs/perfect_dark)) | **Standing reference** — consult it whenever a work item has a PD analogue (same Rare engine family): port-layer ground truth (`port/fast3d/`, crash/system/video), plus copy candidates `port/src/preprocess/` (N64→PC asset conversion; `filemodel.c` is the D43 near-analogue) and `mixer.c`/`input.c`/`fs.c`. Port-layer files only; same family ≠ identical format — validate per field. Full audit: `docs/internals.md` §2.4. |
 
 ## Build