feat: add Qoder harness support (closes #76)

Qoder ships an Agent Skills system at .qoder/skills/{name}/SKILL.md with
slash-command invocation, mapping cleanly onto the existing transformer
pipeline. Adds Qoder as a 13th first-class harness:

- PROVIDER_PLACEHOLDERS entry in scripts/lib/utils.js (model, config_file,
  ask_instruction, command_prefix) mirroring the Pi/Rovo Dev shape.
- PROVIDERS entry in scripts/lib/transformers/providers.js with
  configDir=.qoder and the OpenCode/Claude Code frontmatter field set
  (user-invocable, argument-hint, license, compatibility, metadata,
  allowed-tools), since Qoder docs explicitly support those.
- transformQoder named export in scripts/lib/transformers/index.js for
  test-spy parity (kept per CLAUDE.md guidance, even though build.js uses
  PROVIDERS directly).
- .qoder added to PROVIDER_DIRS in bin/commands/skills.mjs so the CLI
  detects existing Qoder installs.
- HARNESSES.md updated: official docs row, frontmatter support column,
  directory structure row, and "Last verified" date bumped.
- DEVELOP.md reference link added.
- .github/ISSUE_TEMPLATE/feature_request.md and PULL_REQUEST_TEMPLATE.md
  extended with Qoder in the provider checklists.
- Built .qoder/skills/impeccable/ tree committed (per CLAUDE.md harness
  output dirs are tracked so npx skills can read them at install time).

The dynamic providers.test.js loop picks up Qoder automatically; all
non-prefix Qoder cases pass. The pre-existing Windows-only prefix-test
flake affects every provider equally and is out of scope for this PR.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/lib/utils.js

@@ -505,6 +505,12 @@ export const PROVIDER_PLACEHOLDERS = {
     ask_instruction: 'ask the user directly to clarify what you cannot infer.',
     command_prefix: '/'
   },
+  'qoder': {
+    model: 'the model',
+    config_file: 'AGENTS.md',
+    ask_instruction: 'ask the user directly to clarify what you cannot infer.',
+    command_prefix: '/'
+  },
   'trae': {
     model: 'the model',
     config_file: 'RULES.md',