Rename distribution to unity-gateway and generated helpers to ug (Phase 3)

[rohita5l]

Installing from the renamed repository still registers a ucode Python distribution. This completes Phase 3 by registering unity-gateway, while retaining both ug and ucode console commands bound to ucode.cli:main.

• Read CLI/telemetry versions from the renamed distribution and default source-checkout upgrades to its name.
• Update the installation runner's package lookup and dependency snapshots; archived legacy ucode wheels remain supported.
• Document automatic migration, the manual fallback, and recovery after a failed installation. Python imports, saved configuration paths, and telemetry naming stay compatible.
• Update only the root package name in uv.lock; dependency versions are unchanged.
• Generate ug authentication helpers, MCP bridges/web-search commands, and routing hooks across agent integrations, while keeping existing ucode helpers supported. No deprecation warnings are added in this PR.
• Cover canonical helper generation and legacy hook replacement in unit/component tests. Add installed-command protocol checks for both aliases and execute each generated auth helper in the live Claude/Codex Hosted configure journeys.
• Preserve spaces in the integration runner's wheel/constraint paths using file URIs; verified with a real fresh installation under a path containing spaces.

Validation:

• 377 focused tests passed across CLI, entry points, telemetry, doctor, and integration contracts. Ran with the ambient ENABLE_SMART_ROUTING_V2 variable removed from the test process.
• 1,339 affected unit/component tests passed for helper generation, authentication, MCP, agent configuration/routing, CLI, and entry points; 10 integration-contract/evidence tests passed. Used a short macOS pytest temp path and removed the ambient routing override.
• All 5 credential-free installation tests passed against a freshly built wheel in Python 3.12, installed under a path containing spaces. Both aliases emit exact token-only auth output (normal/forced refresh) and preserve MCP JSON-RPC stdout.
• Isolated uv tool install . succeeded, registered unity-gateway, and installed both commands; both --version commands matched its metadata.
• Ruff lint/format, focused production/new-test type checking, and git diff --check passed. An expanded type check also reports 10 diagnostics on unchanged lines in the existing runner/shared protocol harness; those are outside this change.
• All 18 CI checks passed on final head 0d2a536: the full unit suite, installation checks, gateway API tests, all six agent launch suites, and Claude/Codex smoke and full live integration journeys (including the new generated-helper assertions). CI run. Workspace/model e2e tests were not run locally.

Migration notes: installations with the Phase 1 upgrade logic can run ucode upgrade or ug upgrade. uv tool upgrade ucode cannot cross the rename. Older installations need the documented uninstall/install pair. If the replacement installation fails after uninstalling ucode, recovery remains manual; this PR does not add automatic rollback.