docs(skill): add 'Applying changes' section + review polish

Config is loaded once at startup and is not hot-reloaded, but the
skill never said so. Add an 'Applying changes' section so the model
will tell the user to quit and restart opencode after editing config,
agents, skills, or plugins. Mirror that as a final bullet in 'When
proposing edits'.

While reviewing the file, fix a few smaller issues:
- HTML comment referenced SKILL_NAME / SKILL_DESCRIPTION; the actual
  constants are CUSTOMIZE_OPENCODE_SKILL_NAME and
  CUSTOMIZE_OPENCODE_SKILL_DESCRIPTION.
- Replace ambiguous 'or the field is not covered above' with
  'in this skill' (the schema reference is at the top, not above the
  bullet).
- Reword '$schema' paragraph from 'also' (mid-topic-shift) to
  'Independently' for cleaner flow.
- Tighten 'Full schema reference' intro with em-dashes.

Author: kitlangton

packages/opencode/src/skill/prompt/customize-opencode.md

@@ -1,7 +1,8 @@
 <!--
   Built-in skill. Name and description are registered in code at
-  packages/opencode/src/skill/index.ts (see SKILL_NAME and SKILL_DESCRIPTION).
-  The body below becomes the skill's content.
+  packages/opencode/src/skill/index.ts (see CUSTOMIZE_OPENCODE_SKILL_NAME
+  and CUSTOMIZE_OPENCODE_SKILL_DESCRIPTION). The body below becomes the
+  skill's content.
 -->
 
 # Customizing opencode
@@ -12,8 +13,8 @@ is wrong. The shapes below cover the common surface area, but they are a
 
 ## Full schema reference
 
-The authoritative list of every config option, with exact field types, enums,
-defaults, and descriptions, lives in the published JSON Schema:
+The authoritative list of every config option — with field types, enums,
+defaults, and descriptions — lives in the published JSON Schema:
 
 **<https://opencode.ai/config.json>**
 
@@ -22,8 +23,17 @@ shape before writing config, **fetch that URL and read the schema directly**
 rather than guessing. opencode hard-fails on invalid config, so the cost of a
 wrong shape is a broken startup.
 
-Every `opencode.json` should also declare `"$schema": "https://opencode.ai/config.json"`
-so the user's editor catches mistakes as they type.
+Independently, every `opencode.json` should declare
+`"$schema": "https://opencode.ai/config.json"` so the user's editor catches
+mistakes as they type.
+
+## Applying changes
+
+Config is loaded once when opencode starts and is not hot-reloaded. After
+saving changes to `opencode.json`, an agent file, a skill, a plugin, or any
+other config-time file, **tell the user to quit and restart opencode** for
+the changes to take effect. The running session will keep using the
+already-loaded config until then.
 
 ## Where files live
 
@@ -355,13 +365,13 @@ When a user's config is broken and opencode won't start, these env vars help:
 ## When proposing edits
 
 - Validate against the schema before writing. If you are unsure of a field's
-  exact shape, or the field is not covered above, fetch
+  exact shape, or the field is not covered in this skill, fetch
   `https://opencode.ai/config.json` and read the schema rather than guessing.
 - Preserve `$schema` and any existing fields the user did not ask to change.
 - For agent, skill, and plugin definitions, prefer creating new files in the
   correct location over inlining everything in `opencode.json`.
 - If the user's existing config is malformed, point them at the env-var escape
-  hatch above so they can edit from inside opencode without breaking their
+  hatches above so they can edit from inside opencode without breaking their
   session.
-- opencode hard-fails on invalid config by design. There is no graceful
-  degradation, so get the shape right the first time.
+- After saving any config change, remind the user to quit and restart opencode
+  — running sessions keep using the already-loaded config.