docs: mechanical corrections and kelvin refresh

[sigilante]

First of three PRs from an audit of the docs against urbit/urbit@08026c84b2 and urbit/vere@92847eb3fd. This one is deliberately the low-risk batch: mechanical corrections that need no domain review. The other two cover Hoon stdlib signatures and user-manual commands.

Claims were verified against upstream source, and where possible reproduced on a fake ship booted from urbit-408k-rc1.pill ([%zuse 408]).

math.md: 40 corrupted $$ inside code fences

A stray doubling made 34 $( recursion calls and 4 $: bunts invalid Hoon, so every affected listing fails to parse when copied. Confirmed in the dojo:

> =/  i  1  |-  ?:  (gth i 3)  i  $(i +(i))
4

while the $$( form as printed is rejected by the parser outright.

Scope was checked carefully, because a naive replace would do damage:

• the 16 out-of-fence $$...$$ in math.md are LaTeX and are preserved
• stdlib/3b.md, hoon-school/S-math.md and others contain only LaTeX $$ — untouched
• stdlib/4o.md and core-academy/ca02.md contain :: $$, recursion, which is verbatim source ($$ is the %bcbc rune) — untouched

math.md: phantom +exp section

lib/math.hoon:148 is ::++ exp exp:^rs — commented out. The doc dropped the :: and presented it as a live pass-through arm, which also created a duplicate {#exp} anchor colliding with the real +exp. Removed. (The same line is commented out four times in source, once per float core; only the rs one had leaked in.)

Vane count

"nine vanes" → ten, in four files. Lick was missing from the list in arvo/README.md entirely.

Source-block typos

Each checked against sys/hoon.hoon:

File	Arm	Fix
4j.md	+hif:ab	boss → bass
2l.md	+molt	} → ]
4b.md	+rt:at	`$tape` → `tape`
4m.md	+stab	`$path` → `path`
4i.md	+mes	{a/@ b/@} → [a=@ b=@]
1c.md	+bloq	→ $bloq (it is +$ in source); anchor left intact

Note +til legitimately uses +boss, so the +hif fix is deliberately not a global replace. The $tape/$path cases look like a $-prefixing pass that leaked into code blocks.

Runtime and dojo

• vere.md: --scry-info → --scry-into. The long option never existed under the documented name (main.c:303).
• dojo-tools.md: +vat does not exist — verified %generator-build-fail. Dead cross-reference replaced with +vats %base.

Kelvins → 408

Ten illustrative or instructional sites updated. Two of them are commands a reader actually runs (echo "[%zuse 417]" > sys.kelvin in flap.md, same in lick/guide.md); a desk declaring an unsupported kelvin is rejected, so those were not merely cosmetic. Verified |new-desk writes [%zuse 408].

Deliberately not changed — these state when a feature was introduced and remain true: remote scry at 413 and path-format version at 411 (remote-scry.md), %kroc no-op at 410 (hood.md), noun channels at 413 (noun-channels.md), and Core Academy's explicit "snapshot at Zuse 412k".

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