pull syncs nothing in a project whose config cannot be read

[SaulMoro]

Parent

#752 (item 2)

What to build

teamai pull in a project whose config cannot be read syncs nothing and says why. Today detection skips the broken file and uses whatever loads next:

 teamai pull   (project with an unreadable config)
-  → user scope                              reported to the user-scope team
-  → legacy .teamai/ behind a broken partition   another team's skills, rules, docs
+  → nothing synced
+    "Nothing was synced: <file>: <reason>. Fix the file, or move it aside and run `teamai init` to write a new one."
+    exit 1

The session-start hook does the same, silently: no pull, and none of the work around it (agent-root seeding, the package hint). This is the rule hooks and usage already follow since #758. pull is the one path still falling back.

The message must not send the member to teamai doctor: doctor diagnoses the config detection falls back to and says nothing about the broken one.

Acceptance criteria

• A broken partition with a legacy .teamai/ of another team behind it: teamai pull exits 1 with the message above, and no reports-wt/ or learnings-wt/ appears in the legacy .teamai/.
• A broken project config with only a user scope besides it: the user scope is not pulled or reported.
• A session start in such a project: no pull, no seeded agent directory, no package hint.
• A readable project config, or no project config at all: pull behaves as today.
• Verified with the real CLI (Claude, git provider); the usage guide note on project isolation (both languages) and the CHANGELOG say so.

Blocked by

None (can start immediately).