Wire the morphir extension sub-commands to their handlers #492

The morphir extension sub-commands are registered in src/Morphir.Tooling/Scenarios/ManagementScenario.cs, but they never call their handlers. Until 0.4.0-alpha.1 each one printed a stub message and exited 0. For example, install reported success without installing anything, and list always printed "No … installed". From 0.4.0-alpha.1 they fail with a "not implemented yet" error and a non-zero exit code, which links to this issue.

The handlers already exist in src/Morphir.Tooling/Features/Management/ExtensionHandlers.cs:

• list, install <name>, use <name>, remove <name>, which <name> → ExtensionHandlers.HandleList/HandleInstall/HandleUse/HandleRemove/HandleWhich (no unit tests yet)

Scope

• Wire each sub-command to its handler: resolve ArtifactPathResolver (and HttpClient for install) from the CLI's services, map the options (--platform, --local) and print the result.
• Print human-readable results to stdout and send logs to stderr only. Add a --json option if it fits the other commands.
• Serialize any JSON with a source-generated context. The standalone executables are trimmed, and reflection-based JSON fails there (see fix(release): run the deployment E2E tests, fail unimplemented commands, release as 0.4.0-alpha.1 #489).
• Replace the "not implemented yet" error and its tests with real behavior.

Acceptance

• Each sub-command calls its handler and returns the handler's success or failure as its exit code.
• Unit tests for the handlers, plus CLI tests through CliTestHelper (tests/Morphir.Tooling.Tests).
• E2E scenarios in tests/Morphir.E2E.Tests pass against the trimmed executable.

Related: #296 (closed, though the CLI was never wired), #297 (design), #302 (docs and tests), and #493 (archive extraction for install).