feat!: selector mode becomes the default review dispatcher

[bborbe]

Summary

Completes the AI-Selector migration (Steps 4+7, bake deliberately collapsed):

• Default flip: no mode token (incl. standard) → selector mode (in-session classify + adjudicate, zero spawns). short and full unchanged — full mode remains the per-owner deep-sweep escape hatch.
• Dead code removed: standard-mode per-owner Task dispatch (4b-ii) + REVIEW_TIMING instrumentation (−134 lines). The jq glob match stays as the classify candidate source.
• Scenarios 002/004 retired (status: outdated, superseded by 005/006 per their own footers); acceptance checks updated to the new dispatch reality (30/30).

BREAKING-ish: callers passing standard now get selector behavior.

Verification

Tokenless /coding:pr-review master on the bborbe/maintainer#2 fixture (isolated config, plugin pinned to this branch): selector path taken (GUIDE_OK), 2m36s, 19 turns, zero sub-agent spawns, all 5 seeded violations found, traceability 32 candidates → 7 applicable → 25 skipped-with-reasons. make precommit 30/30.

Bake-collapse rationale: 9 validation runs across 4 backends + an organic prod review since yesterday; full mode retained as the per-owner fallback; prod bot already runs selector explicitly via REVIEW_MODE (unaffected by this flip).

🤖 Generated with Claude Code

[ben-s-pull-request-reviewer]

{
  "verdict": "approve",
  "summary": "The selector-mode-as-default flip is correctly implemented across both dispatcher commands. Standard-mode per-owner Task dispatch has been properly removed, selector mode is now the default routing for all non-explicit tokens, the breaking change is clearly documented in CHANGELOG.md, acceptance.sh assertions have been updated to match the post-flip reality, and both retired scenarios correctly reference their superseding siblings.",
  "comments": [
    {
      "file": "commands/pr-review.md",
      "line": 112,
      "severity": "nit",
      "message": "Early exit message ('Step 4 skipped: no rule-relevant files changed') is now mode-agnostic since early exit applies to all modes, not just standard. Consider appending '(all modes)' for diagnostic clarity, though the current text is technically correct."
    }
  ],
  "concerns_addressed": [
    "correctness: argument hint removes 'standard' but callers passing 'standard' now silently get selector behavior — addressed by CHANGELOG.md documenting this as a breaking change",
    "correctness: Step 4d citation validation is now 'Full mode only'; selector mode's citation call lives in the external guide — verified: docs/selector-mode-guide.md lines 65-69 contain citation validation",
    "security: Selector mode guide path resolved from CLAUDE_PLUGIN_ROOT/CLAUDE_CONFIG_DIR env vars — verified: GUIDE_MISSING fail-fast truly blocks and STOPS (reports 'selector guide unavailable' as Must Fix toolchain failure)",
    "correctness: Early exit section no longer labeled 'standard mode' — verified: applies to all modes correctly",
    "correctness: Same argument hint and mode routing changes as code-review.md — verified: both commands have consistent changes",
    "correctness: acceptance.sh assertions updated for new routing — verified: new routing check and tightened per-owner block assertions present",
    "tests: Scenario 002 marked 'outdated' — verified: scenarios/005-selector-clean-short-circuit.md exists with status:active, supersession reference accurate",
    "tests: Scenario 004 marked 'outdated' — verified: scenarios/006-selector-findings-path.md exists with status:active, supersession reference accurate"
  ]
}