docs: overhaul REST API v1 documentation

[Nohzoh]

Description

The REST API v1 documentation was poorly structured, highly repetitive,
and left most objects with no usage examples. This PR rewrites the page
to make it actually useful as a reference.

• Deprecation notice added at the top, pointing readers to the v2 API
• Data model overview explaining all objects and their relationships
• Central object/action reference table as a quick lookup for all
  supported objects and their available actions
• Shared request format — the repeated endpoint URL and auth header
  table that appeared 50+ times are now defined once per section
• Values format explained globally (semicolon-separated fields,
  pipe-separated multiple values)
• add vs set semantics explained once at the top rather than
  inconsistently per-endpoint
• Representative examples added for every object that previously only
  had a bullet list of action names (ACL, ACLACTION, ACLGROUP, ACLMENU,
  ACLRESOURCE, CENTBROKERCFG, CGICFG, CMD, CONTACT, CONTACTTPL, CG,
  DEP, DOWNTIME, HTPL, HC, HG, INSTANCE, STPL, SERVICE, SG, SC,
  TIMEPERIOD, TRAP, VENDOR), including documented values field order
  for each add action
• Authentication section now documents token lifecycle
• Pagination documented with a dedicated section in the Realtime API
• Error response example added to the error codes section
• curl examples added for authentication and the configuration pattern
• State values documented inline (e.g. 0=OK, 2=DOWN, 3=UNREACHABLE)
• Typos fixed: applyed, befores, icone, criticity, fo this,
  event-handfler

Target version (i.e. version that this PR changes)

• 24.04.x
• 24.10.x
• 25.10.x
• 26.10.x
• Cloud
• Monitoring Connectors
• DEM
• Log Management