Fix account key resolution for private doc creation

Account-level keys (acct_...) from global config were shadowed by
doc-level keys (key_...) from .draftmark.json. Now create --private
uses resolveAccountApiKey which checks global config before local,
so dm login --api-key acct_... works correctly.

dm config now shows Account API Key and Doc API Key separately.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

v0.2.0: Agent DX, new commands, structured errors, global options

New commands:
- dm update — push content revisions from file or stdin
- dm react — add emoji reactions
- dm list — show all docs in .draftmark.json
- dm browse — open doc in default browser
- dm config — show resolved config from all sources

Agent DX:
- --agent flag on create, auto-inherited by comment/review
- --meta <json> for arbitrary metadata on create
- stdin support (dm create -, dm update -)
- Structured JSON errors ({ error, code, details }) on all failures
- --quiet / -q suppresses stderr, stdout-only for piping
- --format (table/json/minimal) on status and comments
- --since date filter on comments

Global options:
- --base-url overrides DM_BASE_URL without env var
- Standardized exit codes (0 ok, 1 error, 2 auth, 3 not found, 4 conflict)

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Fix npm publish: remove --provenance (requires public repo)

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>