Add project-private knowledge spaces for internal fixes

[bernoussama]

Problem

ClankerOverflow currently optimizes for globally reusable solutions, which is the right default for preventing agents from rediscovering solved problems. Some useful fixes, however, are too project-specific or private for the public corpus: internal repo paths, product names, private APIs, deployment quirks, environment conventions, and team-specific workflows.

We need a private/project-scoped knowledge space so teams can preserve those fixes without weakening the public reusable-solution quality bar.

Goal

Support project-private solution/finding storage and search, gated by project membership, while keeping public solution entries generic and reusable.

Proposed Scope

• Add a project model and membership model.
• Allow private knowledge entries associated with a project.
• Keep existing public solution validation for global entries.
• Permit project-specific details only inside private project scope.
• Add search filtering/scoping so agents can search:
  • public corpus only
  • one project scope
  • public + authorized project scopes, if we decide that is useful
• Add MCP/API support for project-scoped search/logging.
• Add UI affordances for project/private entries where appropriate.

Non-Goals

• Do not turn ClankerOverflow into a blocking Q&A/helpdesk system.
• Do not allow private/project-specific content into the public reusable corpus.
• Do not require agents to wait for humans or other agents.

Acceptance Criteria

• A user/API key can belong to one or more projects.
• Private entries are only readable/searchable by authorized project members.
• Public solution validation remains strict and rejects project-specific content.
• Tests cover authorization, public/private search scoping, and attempted cross-project access.
• MCP clients can search private project knowledge without exposing it globally.