docs: correct the reasoning-tier keybinding and record the Moonshot CN endpoint

Both findings come from @vFONGv's Windows beginner guide (PR #5229), verified
against the code before landing.

config.example.toml claimed "Shift+Tab in the TUI cycles between off / high /
max". That is stale: crates/tui/src/tui/app.rs:2370 emits the notice
"Shift+Tab now cycles permissions — reasoning effort moved to Ctrl+T". A user
following the config comment would cycle their permission posture while trying
to change reasoning depth, which is the more consequential of the two. His
guide had it right and our own example config had it wrong.

docs/PROVIDERS.md gains his China-region Moonshot finding: a China-region key
needs base_url = "https://api.moonshot.cn/v1" or it fails authentication on the
default international host, and editing base_url alone does not take effect
until `codewhale auth set` is re-run. `api.moonshot.cn` appeared nowhere in the
repo, so this is new information. Recorded as attributed user field evidence
rather than a tested route — we have no China-region key to verify it.

Harvested from PR #5229

Co-authored-by: vFONGv <21223725+vFONGv@users.noreply.github.com>

config.example.toml

@@ -85,8 +85,9 @@ default_text_model = "deepseek-v4-pro"
 # "high"   — reasoning_effort = high (DeepSeek default)
 # "max"    — reasoning_effort = max (deepest reasoning)
 #
-# Shift+Tab in the TUI cycles between off / high / max. The header shows the
-# current tier as a ⚡ chip.
+# Ctrl+T in the TUI cycles the reasoning tier. The header shows the current
+# tier as a ⚡ chip. (Shift+Tab cycles the permission posture — Ask /
+# Auto-Review / Full Access — not the reasoning tier.)
 reasoning_effort = "max"
 
 # NOTE: `show_thinking`, `thinking_default_expanded`, and `cost_currency`