feat: add AdaL as a supported harness agent

[Ricardoran]

Summary

Adds AdaL as a supported harness in the native agent detection registry, with a non-destructive collision guard that never overwrites user-owned skill directories or files.

Changes

File	Change
src/commands/skills-native.ts	Add adal entry to AGENTS array + non-destructive collision guard in symlink phase
README.md	Add adal to harness table + section separating native bootstrap from AdaL marketplace install + collision safety docs
src/__tests__/adal-agent.test.ts	13 focused test assertions (AdaL + cross-harness Codex)

How it works

• firecrawl init --agent adal installs Firecrawl CLI skills to ~/.adal/skills/ as relative symlinks from a canonical ~/.agents/skills/ directory.
• firecrawl init --all auto-detects AdaL by checking for ~/.adal/ existence.
• No Firecrawl API key is required for skill installation.

Collision safety (non-destructive by default)

The symlink-creation phase now handles existing paths as follows:

Existing path type	Behavior
Correct symlink (already points to canonical)	Skip (no-op)
Stale/incorrect symlink	Replace safely
User-owned directory	Skip — never delete (emit warning)
User-owned file	Skip — never delete (emit warning)
Nothing exists	Create symlink

This ensures init --agent adal (including non-interactive mode) never destroys user-authored content at ~/.adal/skills/<skill-name>.

The guard is generic — it protects all harnesses equally (not AdaL-specific). Cross-harness behavior is proven by dedicated Codex collision tests.

AdaL's skill discovery

AdaL's SkillsLoader scans ~/.adal/skills/ for directories containing SKILL.md files with YAML frontmatter (name + description). All Firecrawl CLI skills satisfy this format.

AdaL also has a separate marketplace-based install path (/plugin marketplace add firecrawl/cli) that places skills in ~/.adal/plugin-cache/. The README documents both paths so users can choose — they use different install locations and precedence rules.

Test results

✓ assertion 3+5: adal agent is registered with correct detectDir and globalSkillsDir
✓ assertion 7: auto-detection recognizes existing .adal directory
✓ assertion 8+9: isolated install succeeds and places artifacts in .adal/skills
✓ assertion 10: every installed skill has valid SKILL.md with name+description
✓ assertion 11: preserves pre-existing user-owned skill files with non-conflicting names
✓ assertion 12: idempotent reinstall produces stable result
✓ assertion 13: collision — same-named user directory is preserved, NOT overwritten
✓ assertion 13b: collision — same-named user file is preserved, NOT overwritten
✓ assertion 13c: stale symlinks ARE safely replaced
✓ assertion 14: unwritable destination causes error, no corrupt partial state
✓ assertion 15: paths resolve under isolated HOME, not real HOME
✓ [codex] preserves same-named user-owned directory for codex harness
✓ [codex] preserves same-named user-owned file for codex harness

Test Files  23 passed | 1 skipped (24)
     Tests  403 passed | 1 skipped (404)

All existing tests pass with zero regressions.

Scope of collision guard

The non-destructive guard is applied generically in the installSkillsNative symlink phase (not AdaL-specific). It protects all harnesses equally — any agent with an existing user-owned skill at a same-named path will have it preserved. This is proven by the cross-harness Codex collision tests.

Licensing note

This PR adds only a registry entry pointing to AdaL's existing ~/.adal/skills/ directory convention. No Firecrawl content is redistributed by AdaL.