docs: scrub #NNN self-references (closes #719)

Last pass of the docs-from-code → docs/ epic (#708). Drops every
attribution cookie from docs/ + README.md + CLAUDE.md so the
source-tree files no longer reference the issue tracker. Issue
threads + commit history retain the references — those are the
canonical record.

- README.md: drop #701 / #660×2 / #551 from matrix + display-name
  sections, rephrase to convey the semantics directly
- CLAUDE.md: scrub 18 cookies from the file map (#655, #15, #784,
  #832, #444, #425, #361, #548, #598, #539, #544, #589, #701,
  #658, #280, #660, #551, #764, #772, #793, #14, #805)
- docs/agent-hierarchy.md: drop #658 ×3 (per-agent user is the
  current shape, not a transition)
- docs/conventions.md: drop #571 (replaced with a docs xref to
  persistence.md::matrix-avatar-sync)
- docs/gateway.md: scrub vhost-map table cookies + Sub-domain
  rationale + Per-agent unix-socket upstream + Self-signed TLS +
  Firewall posture + HIVE_FORGE_URL + Per-agent error pages
  sections; drop the trailing 'Sequencing history' issue list +
  the 'Next-up' issue-link footnote
- docs/matrix.md: scrub serverName/gatewayHost + Default-closed
  firewall + Provisioning flow + Initial rollout + Assertion
  rationale + fluffychat-web build fixes; drop the trailing
  'Sequencing history' issue list
- docs/network.md: drop 'Why ship before #14' #805 quote +
  Container shape #805 attribution + trailing 'Sequencing history'
  + Cross-references issue links; rename v2 column to 'after netns
  isolation'
- docs/web-ui.md: drop #784 from Container row, replace with a
  docs xref to docs/gateway.md::Per-agent unix-socket upstream

Only remaining #NNN in docs/ is the literal markdown-heading
example in docs/forge.md (`#tag`, `#123`, `#!/bin/bash`)
which demonstrates the renderer's behaviour — not an attribution
cookie.

docs/agent-hierarchy.md

@@ -251,9 +251,9 @@ boundary.
 ### Environment variables set on the unit
 
 - `HOME = /home/<userName>` — systemd defaults `HOME` to `/` for
-  services without `User=` set; with the per-agent user (#658) the
-  harness needs the right home so claude finds its bind-mounted
-  `~/.claude/` session dir.
+  services without `User=` set; with the per-agent user the harness
+  needs the right home so claude finds its bind-mounted `~/.claude/`
+  session dir.
 - `HIVE_STATIC_DIR = <mergedDist>` — `tower_http::ServeDir` root for
   the per-agent web UI; merged dist = agent default + every
   `hyperhive.frontend.extraFiles` overlay.
@@ -275,9 +275,9 @@ resolve before bare nix-store binaries. NixOS's
 `systemd.services.<unit>.path` appends `/bin` to every entry via
 `lib.makeBinPath`; passing `/run/wrappers/bin` directly produces
 `/run/wrappers/bin/bin` which doesn't exist (`docs/gotchas.md::
-systemd.services.*.path appends /bin to every entry`). Post-#658
-when the harness runs as the per-agent user this matters: without
-the wrapper dir on PATH, `sudo` resolves to the un-setuid nix-store
+systemd.services.*.path appends /bin to every entry`). With the
+harness running as the per-agent user this matters: without the
+wrapper dir on PATH, `sudo` resolves to the un-setuid nix-store
 binary and rejects with `must be owned by uid 0 and have the setuid
 bit set` regardless of `hyperhive.user.passwordlessSudo`.
 
@@ -292,7 +292,7 @@ bit set` regardless of `hyperhive.user.passwordlessSudo`.
   `claude-{mcp-config,settings,system-prompt}` files there
   (`paths::config_dir`). Deliberately separate from `/run/hive`,
   which the host bind-mounts in root-owned and which holds
-  hive-c0re's `mcp.sock` (#658 fixup).
+  hive-c0re's `mcp.sock`.
 - `User = Group = userName` — drops root inside the container; sudo
   is the explicit escalation surface
   (`hyperhive.user.passwordlessSudo`).