docs(changelog): the status-line probe entry no longer says the row draws nothing - #21

Summary

The [0.5.0] section of CHANGELOG.md is the text of the GitHub Release page. After #19, two entries in it disagreed about the status row. This PR rewords the older one (one line).

 ### Added
-- **A probe for the status line (`scripts/tui_pty/status_line_probe.py`, ...)**: it shows that
-  `[ui.status_line]` draws nothing with the Python agent, and that the command script is not run.
-  The row is built from a `session_status` notification that only the old Rust agent sent. ...
-  What to do about it is plan decision 15.
+- **A probe for the status line (`scripts/tui_pty/status_line_probe.py`, ...)**: it starts `zypi` on a
+  pseudo-terminal and looks at the row of `[ui.status_line]`. When it was written, it showed that
+  nothing was drawn with the Python agent ... (4 of 4 runs). ... The row is drawn now (see **Changed**),
+  and the probe checks that: the row is on the screen, and a script gets the facts and no invented number.
 ### Changed
   ...
 - **The status row is drawn with the Python agent (TUI)**: `[ui.status_line]` ... drew nothing ... `zypi` now builds the row ...

The plan (exit condition 5) and the execution log (part 8) get the new size of the notes and one sentence about this check.

Evidence

• Before: awk of release.yml on the section: 49,429 B. It has the line "draws nothing with the Python agent" in Added and the entry "The status row is drawn with the Python agent" in Changed. A reader of the release page gets two answers.
  After: 49,640 B, five groups, same counts (Added 16, Fixed 32, Changed 14, Removed 2, Known issues 6). The words "draws nothing" are gone. The two entries that remain talk about the old state in the past tense ("drew nothing" in Changed, "nothing was drawn" in Added).
• The search for other old lines. I searched the [0.5.0] text for export, status_line, status row, session_status, resume_matrix, GAP, probe and tui_pty, and read each hit. The other hits are about something else (an environment variable that is exported) or are still true (the entry for --session-id says that nothing reads pi/cwd yet; rg finds no pi/cwd in tui/). I also searched the other documents for "draws nothing" and for the old zypi export error text, outside the plan, the log and CHANGELOG.md: no hit.
• ruff check . and ruff format --check . pass. Only text changes.
• Not verified: I did not read the whole [0.5.0] section again for claims that no keyword would find.

Merge Danger

Door: two-way

Only text changes. A revert puts the old line back.

Blast Radius: release notes

The text of the GitHub Release page for v0.5.0. The tag is made from the commit that this PR makes, so the page shows the new text. TUI CI does not start for this PR (its path filter has no document path); CI does.