feat(engine): model-level governance tags inherited from config groups

[hugocorreia90]

What

Adds a model-level [tags] block, inheritable from config groups, so a governance attribute declared once on a group lands on its whole fan-out — completing the engine half of the governed-materialization story (the orchestrator half lands in a follow-up dagster-rocky PR).

# models/groups/finance.toml
schema_template = "mart_{region}"
[tags]
domain = "finance"
tier   = "gold"

# models/fct_orders.toml — inherits domain, overrides tier, adds owner
group = "finance"
[tags]
tier  = "silver"
owner = "data-eng"

→ rocky compile --output json now emits per-model models_detail[].tags:

agg_revenue (.rocky)  tags={domain: finance, tier: gold}
fct_orders  (.sql)    tags={domain: finance, owner: data-eng, tier: silver}

How

• GroupConfig.tags + RawModelConfig.tags + ModelConfig.tags (all #[serde(default)]), merged in resolve_model_config — the shared .sql / .rocky resolution chokepoint, so both loaders inherit for free (the same place enforce lives). Precedence mirrors schema/strategy: the model's own [tags] override the group baseline per key (sidecar > group) without dropping the rest of the group's tags.
• New ModelDetail.tags on the rocky compile JSON output; regenerated schema + Pydantic (rocky-sdk) + TS (vscode) bindings via just codegen.
• 33 ModelConfig literal sites updated (no Default; mechanical empty-map adds).

Verification

• cargo test --all-features green across rocky-core / rocky-compiler / rocky-cli / rocky-ai / rocky-server.
• cargo fmt --check + cargo clippy --all-targets --all-features clean.
• Dual-path proof (guards the feat(engine): config groups — one definition fans out routing + strategy to N models #917-class "wired for .sql only" gap): unit tests on the .sql path (merge precedence + model-only tags), a salsa-loader regression on the .rocky path, and an end-to-end rocky compile check that a .sql and a .rocky member of the same group both resolve the group's tags.

Follow-up

dagster-rocky translator reads ModelDetail.tags and projects them onto the derived AssetSpec.tags (separate PR — the JSON contract this PR establishes is the seam).

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