Usernames and owner-scoped project addresses like GitHub (/owner/project) #351

People (and organizations) get a unique, public handle, and project addresses become /{owner}/{project} instead of /projects/{slug}, as on GitHub. Idea from the user, 2026-09-24 ("evtl": decide before building).

Why now

Public projects (#322) make addresses something people share, link from READMEs and bookmark. Changing the address scheme after projects went public breaks those links, so this should be decided before or together with #322.

Today

• UserAccount has DisplayName (not unique) and PublicId; no handle. Organizations have a Name.
• Project.Slug is globally unique (unique index); a second "Memory MCP" becomes memory-mcp-2. Renaming a project changes its slug and the old address answers not found (ProjectRouteTests asserts this).
• Every web route lives under a fixed first segment: agents, auth, connect, contact, explore, guide, imprint, login, memories, moderation, not-found, organizations, privacy, projects, register, sessions, settings, terms, trust; plus /mcp, /_blazor, /_framework, static files and badge.svg links.
• MCP and .agents/conderis.json use the project id, so agents are not affected by addresses.

Decide first

1. One namespace for people and organizations (like GitHub), so /acme/app works whether acme is a person or an organization? Proposal: yes.
2. Handle rules: allowed characters and length (for example a-z0-9-, 2 to 39, no leading or trailing hyphen), case-insensitive uniqueness, and a reserved list containing every current and planned top-level route (see Today) plus names like admin, api, www, help, support, conderis.
3. Choosing a handle: at sign-up, and for existing accounts on next sign-in. Never derived silently from the sign-in address, since its local part can be personal; a suggestion from the display name that the person confirms.
4. Project names unique per owner instead of globally, with a migration of the unique index. Existing slugs stay as they are.
5. Old addresses keep working: /projects/{slug}/... answers with a permanent redirect to /{owner}/{slug}/..., and so do addresses from before a rename of a handle or project (a redirect table like GitHub's), at least for badge.svg links in READMEs. Decide whether renames keep redirects forever or for a period.
6. Where the owner shows: header path owner / project, sidebar entries only where names clash, Explore, project_get (for example fullName: owner/project), the badge.

Work

• Handle on UserAccount and Organization in a shared, reserved-aware namespace; settings to choose and change it.
• Routes /{owner}/{project} and /{owner}/{project}/{section}/... for every project page; /projects/... redirects.
• Slug uniqueness per owner; creating, renaming and forking follow it.
• Redirects for renamed handles and projects; badge links unaffected.
• Guide, WEB.md routes page (#289) and the smoke test (#345) updated.

Acceptance

• Every project page is reachable at /{owner}/{project}/...; every old /projects/{slug}/... address redirects there permanently. Tested.
• A handle equal to a reserved route name or an existing handle (any case) is refused.
• Two owners can each have a project called app.
• Renaming a handle or project keeps old links and badge.svg URLs working as decided in 5.
• No sign-in address becomes visible through a handle suggestion or an address.