docs(01-01): amend Phase 1 description + Success Criterion #2 per D-A5

Rewrite the Phase 1 one-liner in the Phases list to call out the
chrome.tabCapture -> getDisplayMedia swap, and rewrite Success
Criterion #2 to describe the new operator-selected screen/window
capture and the absence of tab-reattach logic. Phases 2-5 sections are
untouched. The verbatim phrase 'no tab re-attach logic' is preserved
as written in the plan to document the amendment in-place; the
original 'recorder re-attaches to the new active tab' wording is gone.

.planning/ROADMAP.md

@@ -22,7 +22,7 @@ working export → green §10 smoke → harden + clean up**.
 
 Decimal phases appear between their surrounding integers in numeric order.
 
-- [ ] **Phase 1: Stabilize video pipeline** — Collapse offscreen duality, fix MediaRecorder shadow, fix WebM ring buffer playability, make capture always-on with tab re-attach
+- [ ] **Phase 1: Stabilize video pipeline** — Collapse offscreen duality, fix MediaRecorder shadow, fix WebM ring buffer playability, replace `chrome.tabCapture` with offscreen `getDisplayMedia` (AMENDED from original DEC-003)
 - [ ] **Phase 2: Stabilize DOM + event capture privacy** — Migrate rrweb to v2 `maskInputFn`, plug `content/index.ts setupInputLogging` password leak
 - [ ] **Phase 3: Stabilize export pipeline** — Restore user-activation gesture in popup, delete dead `permissions.request`, replace base64 `data:` URL with Blob URL minted in offscreen
 - [ ] **Phase 4: SPEC §10 smoke verification** — End-to-end install-and-record-and-export pass against all 9 acceptance criteria
@@ -55,10 +55,12 @@ directory + `vite.config.ts` inline string + `src/background/`.
   1. There is exactly one source of truth for the offscreen document; rebuilding
      `vite.config.ts` does not regenerate a divergent inline duplicate, and
      `stopRecording` runs without `mediaRecorder is undefined` shadow errors.
-  2. With the extension loaded and a tab open, a single continuous
-     `MediaRecorder` is running on the active tab with timeslice 2000 ms; on
-     tab switch the recorder re-attaches to the new active tab without losing
-     the WebM container header.
+  2. With the extension loaded and an operator session active, a single
+     continuous `MediaRecorder` is running on the operator-selected
+     screen/window source with timeslice 2000 ms; the recorder continues
+     unchanged across tab switches (no tab re-attach logic; AMENDED from the
+     original wording). The WebM container header is retained in the ring
+     buffer indefinitely.
   3. The in-memory video ring buffer at any instant contains the WebM header
      chunk plus the most recent 30 s of subsequent chunks (no more, no less);
      concatenating header + buffered chunks yields a byte sequence a browser