Support project-level marketplaces with override warning

[christso]

Problem

allagents currently stores marketplace aliases in user profile config (~/.allagents/marketplaces.json).

For eval and local workspace scenarios, this creates cross-workspace side effects:

• users may already have a marketplace alias configured globally
• a specific workspace may need a different source (local path vs remote URL)
• changing the global alias affects unrelated workspaces

Goals

• Support workspace-isolated marketplace aliases.
• Keep current behavior backward compatible.
• Make scope explicit in CLI UX.

Proposal

Add project-level marketplace config at:

• .allagents/marketplaces.json (workspace root)

Use the same JSON schema as user-level ~/.allagents/marketplaces.json.

CLI changes

plugin marketplace add

• Add --scope <user|project>
• Default: user (backward compatible)
• Behavior:
  • --scope user writes to ~/.allagents/marketplaces.json
  • --scope project writes to .allagents/marketplaces.json

Examples:

allagents plugin marketplace add ../my-marketplace-repo --scope project
allagents plugin marketplace add https://github.com/org/repo --scope user

plugin marketplace list

• Add --scope <user|project|all>
• Default: all
• Output should identify source scope per marketplace entry.

plugin marketplace remove

• Add --scope <user|project|all>
• Default: all (remove from both scopes if present)

Resolution behavior (runtime)

When resolving plugin@marketplace:

1. Load user marketplaces (~/.allagents/marketplaces.json) if present.
2. Load project marketplaces (.allagents/marketplaces.json) if present.
3. Merge by marketplace name.
4. If both define the same name, project-level entry wins.

Warning behavior

If a project marketplace overrides a user marketplace with the same name, print a warning during resolution/sync, for example:

Workspace marketplace <name> overrides user marketplace of the same name.

Suggested config schema (same as current user file)

{
  "my-marketplace": {
    "source": "local",
    "path": "../my-marketplace-repo"
  }
}

Compatibility notes

• If .allagents/marketplaces.json does not exist, behavior is unchanged.
• Existing user-scoped workflows continue to work with no command changes.

Acceptance criteria

1. add --scope project creates/updates .allagents/marketplaces.json in workspace root.
2. add with no scope still writes user-level config.
3. list --scope all shows combined entries with scope/source indicators.
4. remove --scope project <name> removes only project entry.
5. remove --scope user <name> removes only user entry.
6. remove --scope all <name> removes both entries.
7. Runtime/plugin resolution uses merged view with project-over-user precedence.
8. Override warning is emitted when duplicate name exists in both scopes.