The /session/{id} URL prefix collided with OpenCode's internal
/session/{slug} SPA routes, causing a blank page. Now /c/{id} is
a thin entry point that sets a session cookie and redirects to /,
where the SPA loads at root with its router working correctly.
This also replaces ~50 individual per-path proxy route handlers
with a single /{path:path} catch-all, and simplifies the Caddyfile
from ~180 lines to ~17.
Added proxy routes for all OpenCode internal API endpoints to support
full application functionality when accessed via session manager:
- project, agent, config, model endpoints
- thread, chat, conversation endpoints
- command, mcp, lsp, vcs endpoints
- permission, question, event, status endpoints
- internal session endpoint (distinct from container sessions)
Also updated Caddyfile for routing configuration.
