feat: Subdirectory rule loading when accessing files

[bailey-busc]

What does this PR do?

First pass draft implementation at loading of rules from subdirectories.

Closes #6316

Working

• Loading of subdirectory rules in response to tool calls that introduce files which should result in a rule load
• Path filtering via YAML frontmatter, meaning that rule application can be restricted further to only apply when files matching the globs are in context.
• Configuration under subdirectoryRules option
  • Disabled by default
  • Glob patterns can be set via patterns, default is **/AGENTS.md
  • Searches up by default, can be configured to just load rule files that are in the same directory as the loaded file by setting the exact option to true
• When tool calls that introduced rules into the session are pruned, the rules are also pruned. Tool calls that would match a rule are all tracked, so any live tool calls that reference a rule will keep the rule loaded into the session
• TUI shows rule loads in the message interface, all currently loaded rules are listed in the sidebar

Not working

• Web UI + Desktop UI (Rule loading triggers, just having trouble getting the UI aspect working)

How did you verify your code works?

• Running the TUI, adding additional AGENTS.md files, sending chat messages that should trigger loading of rules
• Simple unit tests

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

I found a potentially related PR:

Related PR:

• Added recursive AGENTS.md loading from child dirs #952 - "Added recursive AGENTS.md loading from child dirs" (Added recursive AGENTS.md loading from child dirs #952)

This PR appears to address similar functionality around loading rules from subdirectories. While it's an older PR, it may contain relevant implementation details or context for the current PR #9657. You may want to review if it was previously merged, closed, or if there's overlap in the approach being taken.