Epic: Best-effort / inheritance search

[AlexAxthelm]

Rewrite of #860 from a single implementation ticket into the umbrella epic for this body of work.
The resolver implementation that used to live here moves to a dedicated child (#869).

Summary

Introduce a best-effort / inheritance model to pathway search. When a user narrows their search to
a specific scope (e.g. "Solar power in Thailand"), show the most specific value each pathway actually
has; if a pathway lacks that exact scope, fall back to the closest broader scope it does have,
rather than dropping the pathway or showing nothing:

Solar · Power · Thailand   (exact)
  → Power · Thailand       (drop technology)
  → Power · South East Asia (loosen geography)
  → Power · Global          (loosen geography)

This is one mechanism applied on two hierarchical axes:

• Geography — country ⊆ region ⊆ global, matched by ISO-3166 code containment.
• Sector / technology — technology ⊆ sector ⊆ cross-sector.

Inheritance affects three things: which pathways appear (broader-scope matches are included
instead of filtered out), ranking (exact scope ranks above fallback), and the value + scope
displayed (the card/detail shows the inherited value with a badge naming the scope it came from).

Motivation

Today filterPathways (src/utils/searchUtils.ts:192) is strict boolean pass/fail — a pathway either
matches every active facet or is dropped, and zero matches yields a blank page. Region definitions vary
across publications and few pathways carry country-level detail, so exact-match search hides pathways
that genuinely have relevant (if broader) data. Best-effort matching surfaces that data with honest
scope labelling.

This epic unifies two efforts from the data-model redesign that were scoped separately: the geography
restructuring (Release 1 / #783) and the metadata restructuring (Release 2 / #858 / #859). They are two
axes of the same scoped-matching engine.

Design decisions

• Scoped fields are per-field arrays of {sector, geography, value} entries.
• keyFeatures vary by sector + geography only (no technology tag). Technology stays a search
  axis, resolved to its sector through the existing sectors[].technologies[] nesting.
• Explicit scope sentinels. Every entry names both axes. Widest geography reuses the real
  "Global" value; widest sector uses a new "cross-sector" sentinel ("cross-region" reserved for a
  multi-region non-global aggregate). The resolver compares fully-specified coordinates.
• On-disk order is irrelevant — priority is recomputed every time from the cost model.
• Fallback ranking = config-driven per-transition cost. Default precedence sector > geography >
  technology ("drop technology first; keep the sector until geography is exhausted at Global").
  Implemented as a single editable cost object so the geography-vs-technology ordering can be flipped in
  one line. Explicitly expected to change once we see it in front of users.
• Schema versioning: new pathwayMetadata.v2.json + a one-time v1→v2 codemod of the ~60 in-repo
  data files. v1 and v2 coexist via $schema $id routing in validateData.ts.

Children

• feature: generalize regions #783 — Geography axis (generalize regions; implemented by PR Feat/geography/data model #836). Sub-tickets: Add pathway regions #799, Add filter region to code base #797,
  Define filter regions #798, Disclaimer about region mappings #800, update pathways to reflect new pathway region geography mapping #801. Delivers ISO-overlap matching = the geography half of the resolver.
• v2 schema + data codemod #858 — v2 schema + data codemod (foundation): scoped keyFeatures, coreDrivers, dependencies,
  pathwayDescription.
• Scope technologies to their sector #461 — Scope technologies to their sector (foundation): the Solar∈Power mapping the search
  axis needs.
• Inheritance resolver engine + search integration #869 — Inheritance resolver engine + search integration (the core algorithm).
• Frontend: scoped values + scope/fallback badges #859 — Frontend: scoped values + scope/fallback badges (folds Distinguish badge style in Key Features more cleanly from badge style in Coverage #852, UI: Key features scale/label alignment #837).
• dataAvailability field + download/link table #870 — dataAvailability field + download/link table (parallel; own design pass).
• Harmonize TypeScript type usage with JSON Schema definitions #597 — Harmonize TS types with schema (rides along with the v2 type regen; related).

Dependency order

#783 (+PR #836) ─┐
#858 ─────────────├─▶ #869 ─▶ #859
#461 ─────────────┘
#870 ── parallel        #597 ── with #858

Out of scope

• Sector-aware restructuring of the metric field (separate future release; structure TBD).
• The non-timeseries "small download" hosting mechanism (tracked in dataAvailability field + download/link table #870 once designed).

Acceptance (epic-level)

• Searching a country (e.g. Thailand) surfaces pathways whose only relevant data is at "South East
  Asia" or "Global" scope, ranked below exact matches, each showing a scope badge for the inherited
  value.
• The blank-search view (no sector/geography filter active) is unchanged.
• All src/data/** validate against v2; type-check + test suites green.