fix(wayfinder): rename "Two branches" to "Two modes"

The word "branch" in the Invocation section primes git-aware agents
(Sonnet, GPT-5.5) to create git branches when running the skill,
littering established environments with per-session branches that then
have to be merged. Nothing here refers to git — the two "branches" are
the two invocation modes (chart the map / work through it). Rename to
"modes" to remove the false cue.

Fixes #418

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skills/in-progress/wayfinder/SKILL.md

@@ -70,7 +70,7 @@ Fog excludes only what's already decided (that's Decisions so far) and what's al
 
 ## Invocation
 
-Two branches. Either way, **every session ends with a [Handoff](#handoff)** — never resolve more than one ticket per session.
+Two modes. Either way, **every session ends with a [Handoff](#handoff)** — never resolve more than one ticket per session.
 
 ### Chart the map