docs/concepts/architecture.md: replaced 8 non-breaking hyphen
characters (U+2011) with regular hyphens. Non-breaking hyphens defeat
copy-paste from rendered HTML, break grep on the raw markdown, and
make Mintlify search miss otherwise-correct queries. Affected words:
'long-lived', 'server-push', 'device-based'.
docs/tools/btw.md: converted the 3-bullet Related list into a
CardGroup. Renamed 'Thinking Levels' to sentence-case 'Thinking
levels' and added a Steer-command card so readers comparing ephemeral
vs in-run intervention paths see both options.
docs/tools/agent-send.md: converted the 3-bullet Related list into a
CardGroup. Removed two em-dash characters in the bullet copy
('Sub-agents — background sub-agent spawning', 'Sessions — how
session keys work') and added a Slash-commands card. Verified
/cli/agent, /tools/subagents, /concepts/session, and
/tools/slash-commands targets all exist.
