Consolidate zero-match recovery to one floored ladder (ADR 0010) + default auto-exposure

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Summary

Executes ADR 0010 (created docs-only in #467): consolidates zero-match recovery to a single fixed-ladder strategy, and resolves the deferred default-regime question by shipping solver-driven auto-exposure as the default.

Recovery consolidation (ADR 0010)

• Recovery is now the single concrete ZeroMatchRecovery class. Deleted the ZeroStarHandler ABC and the Exponential / Reset / Histogram strategies, the set_ae_handler command, the Experimental "AE Algo" menu, and the auto_exposure_zero_star_handler config key (stale config values are ignored).
• Recovery ladder floored at 200 ms → [400, 800, 1000, 200] ms (was 7 rungs down to 25 ms). The floor bounds recovery's blind search only — the match-count controller's feedback clamp still reaches 25 ms.
• Renamed recovery code to the Camera glossary: ZeroMatchRecovery, _zero_match_count, _handle_zero_match, _recovery. The two controllers (ExposurePIDController/ExposureSNRController) and the set_ae_mode:pid/snr wire protocol are intentionally left alone (out of ADR 0010's scope).
• generate_exposure_sweep kept (the diagnostic exposure sweep capture still uses it); docstring updated.

Default exposure regime → "auto"

• default_config.json: camera_exp: 400000 → "auto". Solver-driven auto-exposure now runs out of the box. The ladder starts at 400 ms (the previous fixed default), so the first frame is unchanged. All camera backends + the display callback + daytime-align already handle "auto"; existing users keep their saved camera_exp.
• This was ADR 0010's explicitly-deferred open question; resolved here in favour of auto since the floored single-ladder recovery makes auto-exposure safe by default. ADR 0010 and docs/ax/camera.md §7 now cross-reference the resolution.

Docs & i18n

• Internal: docs/ax/camera.md, docs/ax/camera/CONTEXT.md, docs/adr/0010-* — removed the "until the consolidation lands" hedges, applied the rename, recorded the default-regime resolution.
• User-facing: docs/source/menu_map.rst (removed AE Algo, noted Auto is the default), docs/source/troubleshooting.rst (AUTO-first exposure guidance).
• Re-extracted/compiled translations (the 5 removed UI strings become #~ obsolete entries).

Testing

• pytest -m unit → 453 passed; pytest -m smoke → 5 passed; rewritten test_auto_exposure.py → 22 passed
• ruff check / ruff format --check clean; mypy clean on auto_exposure.py + camera_interface.py
• sphinx-build -n → 0 warnings; pybabel compile clean for all 4 languages
• Live headless boot: app starts on the new default and the Experimental menu shows only SQM / Polar Align / Dev Tools

Note

Removed 3 pre-existing tests in the old TestPIDIntegration that referenced a gains= constructor arg the controller never had — they were unmarked (never collected by pytest -m unit) and would error if run. Can be rewritten against the real gains_increase/gains_decrease API as separate work.

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