Investigate and tame overlapping player light-bar illumination

Outcome: fix excessive accumulated carried-light illumination without changing global exposure or compensating in the HDR tone mapper. Keep single-bar/weak illumination useful, preserve color and existing carried-light shadow semantics, and leave ambient/sun, placed lamps, emission and UI alone unless measured evidence justifies broader scope. This is a general lighting follow-up, separate from HDR PR #2652. Evidence: user supplied same-camera carried lights ON /tmp/pi-clipboard-9ff0f34c-5c88-4695-9cb1-e22541cb9918.png and OFF /tmp/pi-clipboard-084ccd3c-d6ea-436b-bf7e-537604ce8146.png. ON strongly brightens shaded grass, paving and the left building; the upper-right wall changes much less. Player/effect animations differ. This supports carried lights as a substantial contributor but does not establish incoming radiance or overlap coefficients. Pre-HDR lighting clamping hid accumulation; no source-data calibration defect has been demonstrated. Preserved experiment: /home/mathias/.local/share/prk-hdr-backups/deferred-light-overlap-20261013-191814 contains a byte-verified five-file backup/manifest, complete binary patch, private GPU response test sources and test logs. Stash commit 7f6132bbc3fcafe234c7b72b33549e2480ed4afd is based on f2f734123 in engines-client-hdr. It contains a mild combined placed/carried point/spot knee and developer-only F10 carried-light ON/OFF diagnostic with local chat notice. The knee was not visually accepted and must not be treated as the chosen fix. F10's live behavior and developer/production guards were verified. All experiments are excluded from the clean published HDR branch; no experimental validation harness is included in its PR. Next: selectively reuse the diagnostic, not the whole provisional shader policy. Measure carried contribution ranges in the crowded scene and with one nearby wearer; choose a source-specific accumulation policy anchored to those values. Verify weak/dark-scene usefulness, crowded overlap, hue/continuity and shadow semantics with meaningful GPU and user-owned visual checks. No assistant GUI launch. Keep work in a dedicated task branch/commit/PR; do not restore hard SDR clipping or modify individual world assets as a workaround.