docs(guide, glossary): pin each ArgKind's lexical canonical form

Fieldtest spec-gap ratified: Count is a plain positive decimal with no
sign and no leading zeros ('03' refuses) — and the per-kind asymmetry
against TimeOfDay's required zero-pad is deliberate, pinned with its
rationale: canonical is each domain's conventional notation,
fixed-width for wall-clock times, minimal for numbers.

refs #271

docs/authoring-guide.md

@@ -361,8 +361,12 @@ construction-args channel — `args` configures it BEFORE `bind`:
 
 `tz` is `chrono_tz`'s own exact, case-sensitive IANA name (`"berlin"` refuses;
 `"Europe/Berlin"` accepts); `open` is strict zero-padded local `HH:MM`
-(`"9:30"` refuses; `"09:30"` accepts) — the accepted string IS the canonical
-form, no normalization. Giving `Session` no `args` at all refuses the `add`
+(`"9:30"` refuses; `"09:30"` accepts); a `Count` arg (`LinComb`/`CostSum`'s
+arity) is a plain positive decimal — no sign, no leading zeros (`"03"`
+refuses; `"3"` accepts). The accepted string IS the canonical form, no
+normalization — and note the deliberate asymmetry: each kind's canonical
+form is its domain's conventional notation, fixed-width for wall-clock
+times, minimal for numbers. Giving `Session` no `args` at all refuses the `add`
 op (`node <name> is missing required arg "tz"`) — an arg-bearing type never
 silently enters the graph half-configured. `aura graph introspect --node
 Session` lists both declared `arg` rows with their kind and hint text before