Document task frontmatter selectors and -t flag

[Copilot]

PR #88 added two features that were not documented: task frontmatter selectors and the -t flag for emitting task metadata.

Changes

Core Documentation

• README.md: Added sections on task frontmatter selectors field and -t flag with examples
• docs/reference/cli.md: Documented -t flag behavior and output format
• docs/reference/file-formats.md: Documented selectors field syntax, array OR logic, and selector composition

How-to Guides

• docs/how-to/create-tasks.md: Added embedded selectors examples and -t flag usage
• docs/how-to/use-selectors.md: Added comprehensive section on task frontmatter selectors vs command-line selectors
• examples/README.md: Updated with new example tasks

Examples

Added three tasks demonstrating the features:

• implement-go-feature.md: Basic embedded selectors
• write-tests.md: Stage-based filtering
• refactor-code.md: Array selectors with OR logic

Example Usage

Task with embedded selectors:

---
task_name: implement-feature
selectors:
  language: go
  stage: implementation
---
# Implement Feature in Go

Automatically filters rules without -s flags:

# These are equivalent:
coding-context-cli implement-feature
coding-context-cli -s language=go -s stage=implementation implement-feature

View task metadata with -t:

coding-context-cli -t implement-feature

Output includes frontmatter:

---
task_name: implement-feature
selectors:
  language: go
  stage: implementation
---
# Task content...

Original prompt

Update the documentation to cover how to use recently added features.

---

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[alexec]

@swedishborgie just FYI - update the docs.