refactor(hooks): remove dead TheRouter-era exports (markSessionNative, markAlgorithmStarting, setModeToken)

[anikinsasha]

Removes the three exports orphaned by the 7.0.0 retirement of TheRouter.hook.ts (3baba670) — zero callers, imports, tests, or dynamic references on main. Full diagnosis and grep evidence in #1598 (this PR is the mechanical half; the downgrade-guard behavior question stays in the issue).

• hooks/lib/isa-utils.ts: delete 1252-1400 — the orphaned markAlgorithmStarting docblock (1252-1269, physically detached above the wrong function), markSessionNative doc+fn (1270-1315), markAlgorithmStarting fn (1317-1400). The upsertNativeSession alias (1249-1250) and everything from addRatingPulse (1402+) untouched.
• hooks/lib/tab-setter.ts: delete 343-393 — setModeToken JSDoc+fn and LIVE_ALGO_PHASES (362), which only it referenced.

Deletion-only; no behavior change. Deliberately does not touch:

• the isDowngradeFromAlgorithm guard (live — its fate is the open question in TheRouter remnants: three dead exports, and the algorithm→native downgrade block is now unconditional #1598);
• extractModeToken / MODE_TOKEN_RE / PromptProcessing's recovery branch (live E-badge machinery — see TheRouter remnants: three dead exports, and the algorithm→native downgrade block is now unconditional #1598);
• comment rewrites, including the guard comment at isa-utils.ts:1181-1183 that still names the deleted function — those ride a separate wording-sweep PR (in preparation) so the hunks don't overlap.

Testing: bun build LifeOS/install/hooks/lib/isa-utils.ts LifeOS/install/hooks/lib/tab-setter.ts LifeOS/install/hooks/PromptProcessing.hook.ts --target=bun green on this branch (after bun install in LifeOS/install); post-delete git grep for the three symbols returns only historical doc mentions plus the one guard-comment line noted above.