docs(agents): update module paths after directory-form refactor

Update the 'Runtime architecture' section to reflect that state.rs /
cap_portal.rs / state_portal.rs / webrtc.rs are now parent modules of
directory trees:

- src/state.rs -> src/state/mod.rs (+ src/state/dispatch/ for the 13
  Wayland Dispatch impls)
- src/state_portal.rs still exists; helpers split into
  src/state_portal/{bitrate,threads}.rs
- src/cap_portal.rs holds the struct; setup/token_fs/pipewire_thread
  split into src/cap_portal/
- src/webrtc.rs gains src/webrtc/html_page.rs sibling

No content changes beyond the path references; the rest of AGENTS.md
remains accurate.

AGENTS.md

@@ -24,8 +24,8 @@
 - `src/main.rs` is the real entrypoint: parse `Args`, initialize tracing from `RUST_LOG` or `-v`, reject non-H.264, require `--output` or `--port`, detect backend, then run one of two loops.
 - Backend detection in `src/backend_detect.rs`: explicit `--backend portal|screencopy` wins; otherwise wlr-screencopy is preferred when the Wayland global `zwlr_screencopy_manager_v1` exists, else Portal/PipeWire is used if D-Bus ScreenCast is available.
 - Do not use `ashpd` for backend availability checks; `backend_detect.rs` intentionally uses raw `zbus` because `ashpd` caches a `zbus::Connection` in a global and can hang after its owning Tokio runtime is dropped.
-- `src/state.rs` drives the wlroots path using a mio Wayland fd loop and `State<CapWlrScreencopy>`; `src/state_portal.rs` drives the Portal/PipeWire path through `CapPortal` frame channels.
-- `src/webrtc.rs` is a small embedded HTTP/WebRTC signaling server using `str0m`; `--port 0` means file-output mode, `--port > 0` enables WebRTC mode.
+- `src/state/mod.rs` drives the wlroots path using a mio Wayland fd loop and `State<CapWlrScreencopy>` (Wayland `Dispatch` impls live under `src/state/dispatch/`); `src/state_portal.rs` drives the Portal/PipeWire path through `CapPortal` frame channels (bitrate helpers and encode/webrtc thread loops are split into `src/state_portal/{bitrate,threads}.rs`). `src/cap_portal.rs` holds the `CapPortal` struct itself; its setup logic, token filesystem helpers, and PipeWire capture thread live under `src/cap_portal/`.
+- `src/webrtc.rs` is a small embedded HTTP/WebRTC signaling server using `str0m`; the embedded HTML test page is in `src/webrtc/html_page.rs`. `--port 0` means file-output mode, `--port > 0` enables WebRTC mode.
 
 ## Unsafe and FFI work