test(#1976): consolidate 17 agent regression tests into agent-contract suites

Fold 17 issue-named agent-markdown regression files into their canonical agent
suites: agent-frontmatter (shared agent-body-contract catch-all: read-loop guards,
retired-slash-ref bans, sycophancy hardening, doc-writer/code-fixer/review-fix/mapper
contracts, write-truncation), planner-language-regression (planner directive/grep/phase
contract), executor-mvp-tdd-section, verifier-behavior-unverified, intel, and
research-agent-profiles. Verbatim block-scoped describe wrappers; 98 subtests conserved
1:1. All unit (markdown-content) tests — no CLI/env surface. No new files.

Regenerates regression-name allowlist (222->207), ratchets file-count allowlist (intel
entry removed, phase 4->3), makes 13 relocated allow-test-rule exemptions issue-ref-
compliant (ADR-456; prunes stale ids). No CONTEXT.md/ADR refs named the moved files.
lint:ci green.

Part of epic #1969. Closes #1976.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/lint-test-file-count.allowlist.json

@@ -21,15 +21,6 @@
       ],
       "issue": "622"
     },
-    "intel": {
-      "files": [
-        "bug-2351-intel-kilo-layout.test.cjs",
-        "bug-3290-intel-updater-layout-block.test.cjs",
-        "intel-command-cutover.test.cjs",
-        "intel.test.cjs"
-      ],
-      "issue": "TBD"
-    },
     "milestone": {
       "files": [
         "milestone-archive.test.cjs",
@@ -40,14 +31,6 @@
       ],
       "issue": "TBD"
     },
-    "phase": {
-      "files": [
-        "bug-214-phase-researcher-write-truncation-contract.test.cjs",
-        "phase-dependency-levels.test.cjs",
-        "phase.test.cjs"
-      ],
-      "issue": "597"
-    },
     "roadmap": {
       "files": [
         "roadmap-mode-field.test.cjs",