fix(config): allow intel.enabled in config-set whitelist

[abrauchli]

Fixes #2047

Summary

• intel.enabled is the documented opt-in for the intel subsystem (commands/gsd/intel.md, docs/CONFIGURATION.md, docs/FEATURES.md) but it was missing from VALID_CONFIG_KEYS in get-shit-done/bin/lib/config.cjs, so the canonical enablement command failed:

  $ node $HOME/.claude/get-shit-done/bin/gsd-tools.cjs config-set intel.enabled true
  Error: Unknown config key: "intel.enabled"
  

• Adds intel.enabled to the whitelist, documents it under a new "Intel Fields" section in references/planning-config.md (matching the pattern from docs(config): document missing config keys in planning-config.md #1947), and covers it with a config-set test.

• loadConfig in core.cjs derives KNOWN_TOP_LEVEL from VALID_CONFIG_KEYS, so the new intel top-level namespace is accepted automatically with no additional changes.

Test plan

• node --test tests/config.test.cjs — all 65 tests pass, including new sets intel.enabled to opt into the intel subsystem case
• node --test tests/config-field-docs.test.cjs tests/intel.test.cjs — passes
• Manual smoke test in a scratch project:

  $ node .../gsd-tools.cjs config-set intel.enabled true
  {"updated": true, "key": "intel.enabled", "value": true}
  $ cat .planning/config.json
  { "intel": { "enabled": true } }
  

[trek-e]

Review

Blocking: Missing required issue link

Per CONTRIBUTING.md, every fix PR must have a confirmed bug issue with a closing keyword (Closes #NNN, Fixes #NNN, or Resolves #NNN) in the PR body. No issue number appears in this PR description.

Please:

1. Open a bug issue for this regression (config-set rejecting intel.enabled despite it being a documented config key)
2. Add Fixes #NNN to this PR body once the issue is created

Code review (no code issues found)

The fix itself is correct and minimal:

• Adding intel.enabled to VALID_CONFIG_KEYS is the right approach
• The Intel Fields documentation section in planning-config.md follows the same format as other sections
• The test uses writeConfig + runGsdTools + readConfig — correct pattern per CONTRIBUTING.md
• loadConfig derives KNOWN_TOP_LEVEL from VALID_CONFIG_KEYS, so no other changes are needed

Once the issue link is added, this is ready to merge.

[trek-e]

Second-pass verified — 2026-04-10

No new concerns. The original blocking issue stands: this PR has no linked bug issue with a closing keyword in the body. The fix itself is correct. Once a bug issue is filed and Fixes #NNN is added to the PR body, this should be in good shape to merge.

[trek-e]

The only blocker from the previous review — missing issue link — is resolved: Fixes #2047 is now in the PR body.

The fix is correct: intel.enabled added to VALID_CONFIG_KEYS, Intel Fields section documented in planning-config.md, regression test covers the config-set round-trip. Approving for merge.