feat(rules): support installing rules from local files (closes #105)

[Minitour]

Closes #105.

What

Adds a local rule type so rule content can be managed in a separate file instead of inline YAML:

rules:
  - id: typescript-conventions
    type: local
    description: Team TypeScript conventions
    appliesTo:
      - "**/*.ts"
      - "**/*.tsx"
    path: rules/typescript.md

path is resolved relative to the directory containing the capabilities file — the same convention already used by local agents and hooks, so it's consistent across the config.

Note: the issue's snippet paired type: remote with path:. remote already means "fetch from a URL," so this implements the established type: local + path convention instead (matches skills/agents/hooks).

How

• src/types/rules.ts — add 'local' to the Rule type union and a documented path field.
• src/cli/commands/install-tasks/install-rules.ts — extract the per-rule body resolution into an exported, unit-testable resolveRuleBody() and add the local branch (reads the file off disk; throws a descriptive error if path is missing or the file doesn't exist). The writer (installRules) is content-agnostic and needed no change.
• README.md — document the new type with an example in the rules block.

Tests

New install-rules.test.ts covers: local resolution, resolution relative to the capabilities file (not cwd), missing-path error, missing-file error, inline regression, and unknown-type error. Full suite: 1046 pass / 0 fail.

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