Add Pi to databricks aitools install

[lennartkats-db]

Changes

• Register Pi as a skills-only agent (it reads SKILL.md but has no databricks plugin). install/update discover Pi via ~/.pi/agent (honoring PI_CODING_AGENT_DIR) and write Databricks skills into its skills directory, globally and project-scoped (.pi/skills).
• Pi is the first non-plugin agent with project scope, so update --scope project now also picks up agents whose skills live in the project via DetectProjectInstalled (home-based config-dir detection alone misses them).
• Derive the "Supported agents" / skills-only lists in the help text from the registry (SupportedNames/SkillsOnlyNames) so they can't drift as agents are added.
• Add a PI telemetry agent type.

Why

Pi speaks the SKILL.md agent-skills standard, so it can use Databricks skills once they're installed: we just weren't installing for it.

Tests

• Unit tests for Pi's config dir and override (TestPiConfigDir), its global/project skill paths and project detection (TestSkillAgentRegistryPaths, TestDetectProjectInstalled), the registry-derived help (TestSupportedNamesMatchesRegistry, TestSkillsOnlyNamesMatchesRegistry), and update --scope project picking up .pi/skills (TestUpdateProjectIncludesProjectSkillAgents).
• task lint, go build ./..., and the aitools acceptance tests pass.
• Verified end to end against a live model: after databricks aitools install, Pi loads the databricks-core skill in a real session.

[eng-dev-ecosystem-bot]

Integration test report

Commit: e3ed56f

Run: 31376634979

	Env	💚​RECOVERED	🙈​SKIP	✅​pass	🙈​skip	Time
💚​	aws linux	4	4	291	1116	5:11
💚​	aws windows	4	4	293	1114	4:24
💚​	azure linux	4	4	290	1116	5:33
💚​	azure windows	4	4	292	1114	4:42
💚​	gcp linux	1	5	291	1116	5:16
💚​	gcp windows	1	5	293	1114	5:23

8 interesting tests: 4 RECOVERED, 4 SKIP

	Test Name	aws linux	aws windows	azure linux	azure windows	gcp linux	gcp windows
💚​	TestAccept	💚​R	💚​R	💚​R	💚​R	💚​R	💚​R
🙈​	TestAccept/bundle/invariant/no_drift	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
🙈​	TestAccept/bundle/resources/vector_search_endpoints/drift/recreated_same_name	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
🙈​	TestAccept/bundle/resources/vector_search_indexes/recreate/embedding_dimension	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
🙈​	TestAccept/ssh/connection	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
💚​	TestFetchRepositoryInfoAPI_FromRepo	💚​R	💚​R	💚​R	💚​R	🙈​S	🙈​S
💚​	TestFetchRepositoryInfoAPI_FromRepo/root	💚​R	💚​R	💚​R	💚​R
💚​	TestFetchRepositoryInfoAPI_FromRepo/subdir	💚​R	💚​R	💚​R	💚​R

Top 3 slowest tests (at least 2 minutes):

duration	env	testname
3:08	azure windows	TestAccept
2:59	gcp windows	TestAccept
2:58	aws windows	TestAccept

[parthban-db]

LGTM modulo comments.