feat(aura-runner): skipped-tap note; undeclared-tap refusal enumerates declared taps

Two fold-selector fieldtest findings on the --tap seam, RED-first.

Skipped-tap note (#334): an explicit --tap plan replaces the record-all
default entirely (C27: unbound is inert) but gave no runtime signal that
unlisted declared taps went unbound — a forgotten tap surfaced only as a
missing trace file. bind_tap_plan's unbound arm now emits the C14 benign
note (aura: note: declared tap "<name>" unbound this run) per skipped
tap, exit unaffected. No new carrier: the arm is only reachable when
plan.default_named is None (an explicit plan) — under record-all it is
structurally dead, so the default emits nothing. Emitted runner-side
beside the existing eprintln registers; the runner->CLI print migration
is #297.

Undeclared-tap refusal (#333): --tap on a tap the blueprint does not
declare was refused without naming the valid taps, forcing the author
back into the blueprint JSON. TapPlanError::UnknownTap now carries the
declared-tap roster and Display appends it, mirroring UnknownLabel's
fold-roster idiom (C29: a refusal names the closed set it checks
against). Decision minuted on #333 (refusal roster over a new introspect
view).

Rider (#335): the fold roster doc lines now state the summary-row
timestamp — the accumulator folds (count/sum/mean/min/max) land one row
at the last warm (contributing) value's ts, and last gains the same
at-its-own-timestamp wording first already carried. The ratification
record lands in the sibling ledger/glossary commit.

closes #334
closes #333

docs/design/contracts/c27-declared-taps.md

@@ -84,7 +84,12 @@ consumer (`aura-runner::tap_recorder::TapRecorder`) holds the trace store's
 streaming writer in-graph — `initialize` opens (deferred acquisition), `eval`
 appends `(Timestamp, Cell)` (zero per-cycle heap, #77), `finalize` reports
 exactly one terminal outcome; fold consumers (`aura-std::TapFold`) land one
-summary row; live closures run inline (`aura-std::TapLive`). The sweep/reduce
+summary row, stamped with the source value's own timestamp for `first`/`last`
+(they pin a single source instant) and with the finalize timestamp for the
+accumulator folds (`count`/`sum`/`mean`/`min`/`max` summarise a range and have
+no single source instant; `min`/`max` deliberately do not carry the extremum's
+timestamp — ratified as-is, #335); live closures run inline
+(`aura-std::TapLive`). The sweep/reduce
 path never calls `bind_tap`.
 
 The chain-pruning benefit — a sweep paying zero for the study wires behind an