sl0ppty: docs that match the program

Audited every page against the source and the binary rather than against my
memory of it. Eight pages changed; the lists were all fine and the *numbers* were
all wrong.

Checked mechanically, and each of these came out complete: all 37 action names,
all 28 control verbs, all 9 shader names, the expression language's 10 variables,
2 constants and 7 functions, the 8 pane states, every knob the dump prints, every
OSC verb, every internal link and anchor, and every page's place in `docs/nav`.
Every fenced `kdl` block was run through `--check`; every `{"cmd":...}` in an
example is a verb that exists.

What was stale:

- **`make` does not build.** The default goal is `help`, so the install block --
  `make vendor`, `make`, `make test` -- never produced a binary. It says `make
  all` now, timed at 5.5s from clean rather than "about a second".
- **700-odd checks in about eight seconds** is now 1,500-odd in about thirteen,
  plus 260 from the C unit tests, which the sentence did not count at all.
- **About 10k lines of C** is 15k. (10,799 of those are neither blank nor a
  comment, which is presumably where the old figure came from.)
- **Seven chrome presets** are thirteen, and the six new ones use `sin` and `TAU`
  -- so the perimeter section gained the angle idiom it now depends on, and its
  "two things fall out of it" became three.
- **`--check`'s example transcript showed two errors nobody can produce any
  more**: `bad prefix: C-a` and `bad key: ←`. Both inputs became *valid* -- `C-a`
  when the chord parser learned the notation the cheatsheet prints, and `←` when
  it learned the arrow glyphs, precisely so a chord copied off the screen parses.
  Replaced with a transcript I generated, and a note that the problems go to
  stderr, which matters for the pre-commit hook the page suggests.
- **`bell_indicator`** was a real knob documented nowhere.
- **"There is no key for this yet"** about moving a pane between tabs, two commits
  after the keys and the drag landed.
- The cheatsheet's `+N more` line, the finder's `C-u`, and `tab_id` in a pane
  report were all real and unmentioned.

Verified: the whole suite green, `make docs` builds nine pages, and the changed
pages read correctly in a browser -- including the new transcript and the `>` `<`
row of the key table.

1 files changed, 2 insertions, 1 deletions

diff --git a/docs/panes.md b/docs/panes.md
index 40ea565..95bcdc5 100644
--- a/docs/panes.md
+++ b/docs/panes.md
@@ -49,7 +49,8 @@ nothing you click can disagree with what is on screen.
 Tabs stop being navigation somewhere around six projects. `C-a f` opens a picker
 over the whole session — every tab, including panes a small window has collapsed
 out of sight. Type to narrow it by pane title, tab name or
-[purpose](layouts.md#purposes); arrows, `C-n`/`C-p` or tab to move; enter to go.
+[purpose](layouts.md#purposes); arrows, `C-n`/`C-p` or tab to move, `C-u` to clear
+what you typed, enter to go.
 A dot marks where you already are.
 
 ## Panes that were given a command