docs: the file viewer, the Tasks page, profiles and user administration

Four gaps off the coverage map, written for the in-app assistant:

- file-viewer.md — what each kind renders to, the live reload, editing a
  Markdown file and the conflict banner, git history mode, and why a `.tex`
  must be shown instead of a PDF built from it.
- tasks-page.md — the four sections, disable-vs-delete, where each kind's
  result lands, and that there is no "new task" button because tasks are
  created in conversation.
- profile.md — display name, language, password, and what an encrypted
  account means when the password is forgotten.
- users.md — creating a member and the irreversible encryption choice, the
  directory profile that feeds the agents' prompt, deactivating vs deleting,
  and the per-person event-triage interval.

Indexed in docs/index.md, cross-linked from files.md, tasks.md and access.md.

docs/access.md

@@ -37,4 +37,4 @@ The three things being granted are not the same, and the difference matters when
 - **A shared connector grant** (one the admin runs centrally, e.g. web search) puts that connector's tools in that person's assistant.
 - **A per-user connector grant** (e.g. Gmail, WhatsApp) only authorizes the person to *set it up* — they still have to sign in with their own account. Nobody ever uses somebody else's credentials through a grant.
 
-See also: [index.md](index.md) for the plugin list, and each plugin's own page under [`plugins/`](plugins/).
+See also: [index.md](index.md) for the plugin list, each plugin's own page under [`plugins/`](plugins/), and [users.md](users.md) for the rest of a person's page — the account itself, their directory profile and their schedule.