bug: `apm mcp search/list/show` ignore `MCP_REGISTRY_URL` env var

[danielmeppiel]

Summary

MCP_REGISTRY_URL is honoured on the install path (via SimpleRegistryClient.__init__ fallback chain) but ignored by the discovery commands, which hardcode the public registry URL.

Where

• src/apm_cli/commands/mcp.py:32, 117, 304 instantiate RegistryIntegration("https://api.mcp.github.com")
• Should match src/apm_cli/install/default_manager.py:115 which calls RegistryIntegration() with no arg, letting SimpleRegistryClient apply the env-var fallback (registry/client.py:19-21)

Impact

Enterprise users pointing APM at a private MCP registry get inconsistent behaviour: apm install --mcp <id> resolves against their internal registry, but apm mcp search, apm mcp list, and apm mcp show keep hitting the public api.mcp.github.com. Discovery is broken for internal-only servers.

Fix

Drop the hardcoded URLs in commands/mcp.py -- construct RegistryIntegration() with no arg in all three call sites.

Docs

Behaviour is documented as a temporary asymmetry in guides/mcp-servers.md (PR #811). Drop the caution callout once this lands.

Found while documenting MCP_REGISTRY_URL in PR #811.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[danielmeppiel]

Fixed in PR #810 (commit a4b3d21).

apm mcp search/list/show now construct RegistryIntegration() with no positional URL, so the existing MCP_REGISTRY_URL fallback in SimpleRegistryClient fires uniformly across all apm mcp commands and apm install --mcp.

Additional polish:

• Muted Registry: <url> diagnostic when the env var is set (defaults stay quiet, overrides are visible).
• Network errors name the configured URL and hint at MCP_REGISTRY_URL so misconfigured enterprise registries are obvious instead of looking like network flakiness.
• Docs (mcp-servers.md, cli-commands.md, apm-usage skill) updated; the stale :::caution callout is gone.

Hardening items raised by the supply-chain security review (URL validation, http:// rejection, fail-closed on overrides) are tracked separately as #814 since they are intentional behaviour changes that warrant their own review.