Update pkg/codingcontext/README.md to reflect current API

[Copilot]

The package README documented API that no longer exists and was missing documentation for types and functions added in recent releases.

Changes

Fixed Examples

• Replaced non-existent WithWorkDir with WithSearchPaths
• Removed obsolete WithRemotePaths and WithEmitTaskFrontmatter options
• Added new options: WithAgent, WithResume, WithUserPrompt, WithManifestURL
• Updated frontmatter access from map-based to typed struct fields

Before:

ctx := codingcontext.New(
    codingcontext.WithWorkDir("."),
    codingcontext.WithRemotePaths([]string{"..."}),
)

After:

ctx := codingcontext.New(
    codingcontext.WithSearchPaths("file://.", "git::https://..."),
    codingcontext.WithAgent(codingcontext.AgentCursor),
    codingcontext.WithUserPrompt("Additional context"),
)

Added Missing Documentation

• Types: Agent, TaskFrontMatter, RuleFrontMatter, CommandFrontMatter, BaseFrontMatter, MCPServerConfig, MCPServerConfigs, TransportType, task parser types
• Functions: ParseTask, ParseParams, ParseAgent
• Constants: Agent constants (AgentCursor, AgentOpenCode, etc.), TransportType constants, FreeText constants
• Methods: (*Result).MCPServers(), methods on Params/Selectors/Agent types

Updated Type Signatures

• Markdown is now generic: Markdown[T any] with type aliases TaskMarkdown and RuleMarkdown
• ParseMarkdownFile signature changed to: ParseMarkdownFile[T any](path string, frontmatter *T) (Markdown[T], error)
• Result struct now includes Tokens int and Agent Agent fields

Removed Obsolete Documentation

• Functions: AllTaskSearchPaths, AllRulePaths
• Options: WithWorkDir, WithRemotePaths, WithEmitTaskFrontmatter
• Types: Generic FrontMatter map (replaced by structured types)

Original prompt

Review pkg/codingcontext/README.md and verify it is up-to-date.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[Copilot]

Pull request overview

This PR updates the pkg/codingcontext/README.md to accurately reflect the current API after several breaking changes. The documentation was outdated with references to removed functions and missing documentation for new types and methods.

Key changes:

• Replaced obsolete API examples (WithWorkDir, WithRemotePaths) with current options (WithSearchPaths, WithAgent, WithUserPrompt, WithManifestURL)
• Added comprehensive documentation for 15+ new types including Agent, frontmatter types, MCP server configs, and task parser types
• Updated type signatures to reflect the generic Markdown[T] implementation