canon: DOLCHEO cleanup — supersede DOLCHE doc, note O/O-open intentional collision

[klappy]

Two small follow-ups after PR #112 landed the DOLCHEO umbrella. Both items were captured as open threads ([O-open P3] and [O-open P4]) in the PR #112 validation ledger.

1. Supersede the DOLCHE doc

docs/oddkit/proactive/dolche-vocabulary.md was showing status: active despite being explicitly superseded by canon/definitions/dolcheo-vocabulary.md. The umbrella's supersedes: field established the relationship from the authoritative side but the older doc had no matching signal.

Changes:

• status: active → status: superseded
• Adds superseded_by: canon/definitions/dolcheo-vocabulary.md (inverse pointer to the umbrella's supersedes:)
• Adds a banner blockquote at the top of the body pointing readers at the DOLCHEO umbrella while preserving the doc as the canonical description of the six-dimension pattern

Note: status: superseded and the superseded_by field are newly exercised in this repo. The current frontmatter schema (canon/meta/frontmatter-schema) lists status: active | proposed | final and documents supersedes but not superseded_by. If this becomes the standard pattern, a follow-up should update the schema. For now, these are the logical inverse of existing fields and self-describing.

2. Acknowledge the intentional O/O-open collision

odd/encoding-types/how-to-write-encoding-types.md tells custom-type authors: "Letter should not collide with existing types (D, O, L, C, H, E)." That's been correct for the default set until DOLCHEO introduced the intentional collision between Observation (closed) and Open (forward-pointing), both registered under letter O with facet-based disambiguation.

Changes:

• One-line-expanded convention that flags the O/O-open case as the one allowed exception, explains how it's resolved (facet field plus section placement), and tells custom-type authors they can follow the same pattern if their domain genuinely needs a collision.

Verification

• git diff --stat: 2 files, +7/-2 lines
• Frontmatter native YAML types preserved
• No other content changed

Ready to merge once CI is green.

---

Note

Low Risk
Low risk: documentation-only updates that don’t affect runtime behavior; the only potential issue is tooling that assumes a limited status/frontmatter schema.

Overview
Marks docs/oddkit/proactive/dolche-vocabulary.md as superseded (adds superseded_by and a top-of-doc banner) to direct readers to the canon/definitions/dolcheo-vocabulary.md umbrella.

Updates odd/encoding-types/how-to-write-encoding-types.md to explicitly document the intentional O letter collision between Observation and Open and how it is disambiguated (via facet: open and ledger section conventions).

^{Reviewed by Cursor Bugbot for commit f6c1e4f. Bugbot is set up for automated code reviews on this repo. Configure here.}