Add E2E Spec

Create a new E2E_TESTS.md specification file for a package by analyzing its source code, commands, and public API.

Additional instructions from the user: "$ARGUMENTS". Ignore if empty.

Phase 1: Analyze Package

1. Identify the target package:

   • If $ARGUMENTS specifies a package path, use that.
   • If in a package directory, use the current package.
   • Otherwise, ask the user which package to analyze.

2. Read the package to understand:

   • What the package does (README, package manifest, main entry points)
   • Public API / exported commands / CLI interface
   • External dependencies (what it calls: Docker, HTTP APIs, CLI tools)
   • Configuration files it reads or creates
   • State it manages (databases, file stores, caches)

3. Check if an E2E_TESTS.md already exists for this package. If it does, inform the user and suggest using update-spec instead.

Phase 2: Draft Spec

1. Determine the suites. Each major command, workflow, or feature area becomes a suite.

2. Include an Index section at the top of the spec (after the title and description) with a markdown link to every suite (e.g., - [Suite Name](#suite-name)).

3. For each suite, draft these sections using heading levels appropriate to their nesting depth (e.g., if the suite is an H2, then these sections are H3; if the suite is an H3, they are H4; and so on):

   • Preconditions (heading with bullet list): What setup is needed (temp dir, git repo, config files, mock tools)
   • Features (heading) containing individual features as flat peer subheadings one level deeper. Do NOT create intermediate category headings (e.g., #### Core, #### Edge) — categories are specified only via <!-- category: ... --> HTML comments on each feature. Aim for a mix of features across these categories:
     • core: Primary happy-path scenarios
     • edge: Boundary conditions (empty inputs, very long strings, special characters)
     • error: Failure modes (missing config, invalid input, unavailable dependencies)
     • side-effect: Observable interactions (hooks, notifications, file creation)
     • idempotency: Safe repetition (re-running commands, re-creating resources)
   • Postconditions (heading with bullet list): Verifiable end states

4. For features requiring real external services, add <!-- skip: ... --> metadata with clear documentation on how to unskip.

5. Ensure every feature has:

   • A <!-- category: ... --> comment
   • At least one concrete, testable assertion bullet
   • Present tense, declarative language

Phase 3: Review

1. Present the complete draft spec to the user.
2. Show a summary:
   • Number of suites
   • Features per suite by category
   • Total feature count
   • Any features marked as skip
3. Ask the user for feedback and adjustments.

Phase 4: Write

1. Write the approved spec to E2E_TESTS.md in the package directory.
2. If a root-level docs/E2E_TESTS.md or E2E_TESTS.md doesn't exist yet, offer to create one with project-wide testing constraints (isolation rules, cleanup patterns, environment variable conventions).
3. Inform the user they can now run:
   • review-spec to validate the format
   • generate to create test files from the spec