docs: record the semantic palette landing, and one claim that was false

The two findings recorded as too big for the contrast pass are fixed, so
the plan says so. Also corrects a claim I made and did not check: the
chrome does not stay dark under the light ramp -- that screenshot was
taken before the theme propagated, which is the third time in two passes
a picture read at the wrong moment produced a confident wrong claim.

.planning/NOTES.md

@@ -1954,3 +1954,77 @@ Nine things worth keeping:
   and every one was a *different* mechanism. A finding at 110 nodes
   hides them; at 3 they are individually obvious. Cheap tail, only
   reachable from the other side of the main fix.
+
+## A role, not a value, decides whether a colour can be fixed
+
+Plan 008 phase 2, third landing: the two findings the contrast pass had
+recorded as too big to fix in it, fixed — plus the check for the trap
+that has now cost four sessions.
+
+The generalisation: **a token that is used for two different jobs will
+be wrong at one of them, and no amount of choosing a better value
+fixes it.** `--yj-error` was "the colour of error", which is two
+questions. As the *background of a danger button* it wants to stay red
+in every theme, and it does. As *the word `failed` on a surface* it
+cannot be one value at all — a single colour cannot clear 4.5:1 against
+both a near-black and a near-white background, which is why the fixed
+set measured 2.31–4.28:1 on nearly every combination. Splitting the
+token by the question it answers made both answerable; picking better
+hexes never would have.
+
+The same shape twice more in the same landing:
+
+- **A fill's foreground cannot be written down**, because the accent is
+  a colour picker. `color: #000` is right for the current default
+  yellow and wrong for a navy one. `readableOn()` computes it — white
+  where white clears 4.5:1, black otherwise — which keeps a red danger
+  button conventional (4.51:1) and flips a green one (3.45:1).
+- **`var(--yj-bg-base)` as a foreground is a token used for the wrong
+  meaning.** Two accent buttons did that. It reads as "the opposite of
+  the accent" and it is not: it inverts with the ramp, so the light
+  theme rendered white on yellow at 1.43:1. The bug is not the value,
+  it is that the *name* did not mean what the call site needed.
+
+Six more things worth keeping:
+
+- **The picture and the number disagreed, and the number was mine —
+  again.** I recorded "the header and player chrome stay dark while the
+  body goes light" as a finding, in the plan and in these notes. It is
+  false: `.top-bar` is `#e9ecef` and `.sidebar` `#f8f9fa` under the
+  light ramp, and a re-taken screenshot agrees with the DOM. The
+  original was captured before the theme had propagated. That is the
+  third time in two passes a screenshot read at the wrong *moment*
+  produced a confident wrong claim, after a spec reading the DOM before
+  a fetch and a sweep that had moved the app to another ramp. **A
+  screenshot has a timestamp and a state; check both before quoting
+  it.**
+- **A `color:` regex matches `border-color:`.** Twice in one landing —
+  3 borders while rewriting semantic text, then 30 more while rewriting
+  accent text. Both caught by grepping the *result*, not by any test,
+  because a border in the wrong shade fails nothing and looks fine.
+  When a mechanical rewrite is the right tool, the review is a grep of
+  what it did, not a run of the suite.
+- **A fix at the ubiquitous case makes the rare ones findable.** The
+  greyscale fix took the dark ramp to 0 and the light ramp from 50 to a
+  list short enough to read individually — at which point every
+  remaining item was a *different* mechanism, and two of them were the
+  findings above. A queue of 110 hides its own structure.
+- **Knowledge that has been ignored three times is not a knowledge
+  problem.** The backtick-in-a-`css`-comment trap is documented in
+  `CLAUDE.md`, in the skill and here; I read it twice in the session it
+  then cost a cycle in. It is `make css-check` now — a pre-commit hook
+  and a CI step. The detection is exact rather than heuristic: if a
+  backtick in a comment closed the literal early, the text the parser
+  took as the literal contains an unterminated `/*`, and nothing else
+  produces that.
+- **The value of that check is the sentence, not the failure.** `tsc`
+  already failed on it — with `Class static side 'typeof NowPlaying'
+  incorrectly extends base class static side` and `Property 'scroll'
+  does not exist on type 'CSSResult'`, pointing at a line of prose. The
+  check was verified by breaking a file on purpose and reading both
+  reports side by side, which is also the only way to know it fires.
+- **A change can be invisible to the tier that looks the most like it
+  covers it.** `make ui-visual` passed unchanged through a whole
+  palette rewrite, twice, because the component tier has no `:root` and
+  renders the fallbacks. The tier that *did* catch things was a unit
+  test over the palette table and a probe against the running app.