[Sync] Named connections with --tag for disambiguating multiple connections per platform

[siddharth-bhansali]

Context

Sync profiles today pin to a connection in one of two ways:

1. Hardcoded connectionKey (legacy) — "connectionKey": "live::gmail::default::abc123". Breaks silently when the user re-auths and a new key is generated.

2. Late-bound connection ref (v1.41.0) — "connection": { "platform": "gmail" }. Resolves at runtime, but fails when the user has multiple connections for the same platform:

   Multiple "gmail" connections found. Add a "tag" field to disambiguate.
   

There's no clean way to wire a profile to a specific connection among several on the same platform without falling back to the stale connectionKey approach.

Proposed pattern: named connections

1. Tag connections at creation time:

   one add gmail --tag personal
   one add gmail --tag work

2. Sync profiles reference by platform + tag:

   {
     "connection": { "platform": "gmail", "tag": "personal" }
   }

3. If only one connection exists for a platform, tag stays optional (current behavior).

4. one add gmail --tag personal on an existing tagged connection refreshes it in place rather than creating a duplicate.

What this eliminates

• Stale connection keys in profiles after re-auth
• Duplicate connections from one add on an existing platform
• The need for external resolvers (several users have built wrapper scripts for this)
• Ambiguity when multiple connections exist for the same platform

Scope

• one add <platform> --tag <name> — create or refresh a tagged connection
• one connection list — show tag column
• connection: { platform, tag } — recognized in sync profile schema
• Documentation updates: guide sync, skills/one/SKILL.md, README

Raised in knowledge repo issue withoneai/knowledge#69 — breaking out here since it's CLI-scoped.