docs(admin/occ): complete DAV & database command documentation

[miaulalala]

New DAV commands:

• dav:absence:get/set — manage out-of-office absence settings
• dav:clear-calendar-unshares — clear stale calendar unshare records
• dav:clear-contacts-photo-cache — clear cached contact photos
• dav:list-calendar-shares — list calendar shares, with --calendar-id filter

New database commands:

• db:add-missing-columns — add optional columns missing from schema
• db:add-missing-primary-keys — add primary keys missing from schema
• db:convert-filecache-bigint — convert filecache IDs to BigInt
• db:convert-mysql-charset — convert MySQL/MariaDB tables to utf8mb4
• db:schema:export — export current database schema
• db:schema:expected — export expected schema for fresh installation

Writing quality improvements:

• Eliminate "Misc" catch-all section; give each command a proper heading
• Standardize all example user names to layla
• Fix dav:create-subscription example (remove stray 'calendar' argument)
• Update command summary listing with all new commands
• Standardize heading style to command-name headings throughout
• Restructure database section: schema maintenance, schema inspection, and data conversions subsections
• Expand db:add-missing-indices entry to mention --dry-run

AI-Assisted-By: Claude Sonnet 4.6 noreply@anthropic.com

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