feat: integrate Leptos 0.8 SSR into daemon — single port serves API + web frontend

Upgraded Leptos from 0.7 to 0.8 to unify axum version (both now use axum 0.8).

`flowctl serve --port 3000` now:
- Serves REST API on /api/v1/* (existing daemon routes)
- Renders Leptos SSR on all other routes (fallback)
- Single process, single port, no separate frontend server

Changes:
- flowctl-web: Leptos 0.7 → 0.8 (leptos, leptos_meta, leptos_router, leptos_axum)
- flowctl-cli: Added leptos + leptos_axum + axum as daemon-gated deps
- flowctl-daemon: Made build_router() and create_state() pub for CLI integration
- Cargo.toml: Added [[workspace.metadata.leptos]] config for cargo-leptos
- main.rs: serve_tcp now builds combined API + Leptos SSR router

All targets compile: default, hydrate (WASM), SSR, daemon.
0 clippy, 224+ tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: z23cc