Implement AT-SPI selection bridging groundwork

Add the document selection adapter, integrate it through script utilities and major callers, and package the clipboard fallback work that was needed during manual testing on Wayland.

Also include a handoff note for the still-open browser link-selection issue so other developers can continue from the current branch state without reconstructing the debug trail.

docs/atspi-document-selection-handoff.md

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+# AT-SPI Document Selection Branch Handoff
+
+Branch: `atspi-document-selection`
+
+## Implemented
+
+- Added document-wide AT-SPI selection normalization in
+  `src/cthulhu/ax_document_selection.py`.
+- Reworked text-selection handling in `src/cthulhu/script_utilities.py` to use
+  the shared adapter where possible and fall back cleanly where not.
+- Updated primary callers in the default and web scripts so copy/cut,
+  selection announcements, and selected-text queries use the shared selection
+  path.
+- Added keyboard-driven clipboard announcement fallback in
+  `src/cthulhu/scripts/default.py`, including Wayland-specific policy changes.
+- Fixed `build-local.sh` so rebuilding refreshes modified installed modules
+  under `~/.local`.
+
+## Verified
+
+- `python3 -m pytest -q tests/test_document_selection_regressions.py`
+- `python3 -m pytest -q tests/test_default_script_clipboard_regressions.py`
+- `python3 -m pytest -q tests/test_web_input_regressions.py`
+- `HOME=/tmp/cthulhu-test-home python3 -m pytest -q tests`
+- `./build-local.sh`
+
+Latest full-suite result before handoff: `95 passed, 1 warning`.
+
+## Still Open
+
+- Browser link-text selection is still not reliable in Chromium/Edge and in
+  web-backed content like Steam.
+- The current branch includes extra diagnostics around clipboard and selection
+  paths because they were useful during manual debugging.
+- The newest attempted web fix is in `src/cthulhu/scripts/web/script.py`, but
+  the manual repro still fails:
+  - selecting link text with `Shift+Left` / `Shift+Right`
+  - hearing no selection announcement
+  - then having copy behavior depend on fallback logic instead of real
+    selection state
+
+## Useful Files For Follow-Up
+
+- `src/cthulhu/ax_document_selection.py`
+- `src/cthulhu/script_utilities.py`
+- `src/cthulhu/scripts/default.py`
+- `src/cthulhu/scripts/web/script.py`
+- `src/cthulhu/scripts/web/script_utilities.py`
+- `tests/test_document_selection_regressions.py`
+- `tests/test_default_script_clipboard_regressions.py`
+- `tests/test_web_input_regressions.py`