docs: fix schedule frequency list in update-workflow validation checklist (#1629)

Plain `weekly` (any day, scattered time) is a valid fuzzy schedule
frequency — supported in src/fuzzy_schedule.rs and documented in
docs/schedule-syntax.md — but was omitted from the validation checklist
in prompts/update-ado-agentic-workflow.md.

Also adds the long form `every N hours` alongside the short `every Nh`
for completeness.

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Author: github-actions[bot]

prompts/update-ado-agentic-workflow.md

@@ -309,7 +309,7 @@ Before finalizing any update, verify:
 
 2. **MCP allow-lists**: Custom MCP servers (with `container:` or `url:`) have explicit `allowed:` lists.
 
-3. **Schedule syntax**: The schedule expression uses valid fuzzy schedule syntax. Valid frequencies: `daily`, `weekly on <day>`, `hourly`, `every Nh`, `every N minutes`, `every N days`, `every N weeks`, `bi-weekly`, `tri-weekly`. Valid time specs: `around HH:MM`, `between HH:MM and HH:MM`.
+3. **Schedule syntax**: The schedule expression uses valid fuzzy schedule syntax. Valid frequencies: `daily`, `weekly`, `weekly on <day>`, `hourly`, `every Nh` / `every N hours`, `every N minutes`, `every N days`, `every N weeks`, `bi-weekly`, `tri-weekly`. Valid time specs: `around HH:MM`, `between HH:MM and HH:MM`.
 
 4. **Repository aliases**: Every repo alias used in agent instructions or safe-output `repository:` fields exists as an entry in `repos:` with `checkout: true` (the default).