docs: marketplace index + README (adds AI-skill-pack provenance)

README.md

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+<p align="center"><img src="assets/skillfactor_logo_red.png" alt="skillfactor" width="360"></p>
+
+# skillfactor marketplace
+
+**AI with work experience.** The occupational skill layer: public occupation
+databases (ESCO, O*NET) + live job-ad evidence + expert knowledge, compiled
+into one ready-to-use skill package per occupation. Every employee agent loads
+the package for its role — and starts with the profession built in.
+
+**3039 occupations** are currently published in
+[`skills-core`](https://zeiterfassung.cloud/skillfactor/skills-core). The machine-readable index is
+[`marketplace.json`](marketplace.json).
+
+## Architecture
+
+```mermaid
+flowchart LR
+    A["ESCO 1.2.1 / O*NET 30.3<br/>+ official crosswalk"] --> DB[("evidence store<br/>Microsoft SQL Server")]
+    J["job ads<br/>(JSearch / Adzuna APIs)"] --> DB
+    W["Wikipedia / Wikidata<br/>+ literature"] --> G
+    DB --> G["generator"]
+    G --> CORE["skills-core<br/>1 repo per occupation"]
+    CORE -->|fork| T["tenant-acme<br/>(private extensions)"]
+    T -->|sanitize gate:<br/>PII scan + eval + human PR review| COMM["skills-community"]
+```
+
+## Layer model
+
+| Layer | Content | Visibility |
+|---|---|---|
+| community | shared, anonymized best practices | public |
+| company | tenant processes (e.g. `tenant-acme`) | private |
+| role | the role's memory | tenant |
+| person | personal style | employee |
+
+Every boundary is a gate: PII/secret scan (`sanitize.yml`), structural eval
+(`eval.yml`), anonymization, and a human pull-request review.
+
+## Data provenance
+
+Every package documents where its content comes from in its own
+`PROVENANCE.md` (rendered pie chart + table). Library-wide distribution of
+content items:
+
+```mermaid
+%%{init: {'theme':'base','themeVariables':{'pie1':'#f9a825','pie2':'#1e88e5','pie3':'#ff355e','pie4':'#43a047','pie5':'#8e24aa','pie6':'#00acc1','pieOuterStrokeWidth':'0px','pieSectionTextColor':'#fff'}}}%%
+pie showData
+    title Content sources across all 3039 packages
+    "ESCO (occupations & competences)" : 129090
+    "O*NET (tasks & tools)" : 254144
+    "Job boards (market evidence)" : 168044
+    "Wikipedia & AI expert curation" : 154
+    "External AI skill packs (mapped)" : 360813
+    "Stack Exchange practitioner Q&A (CC-BY-SA)" : 1500
+```
+
+The taxonomy share dominates library-wide because job-ad and expert
+enrichment rolls out occupation by occupation (see the
+[recruiter package](https://zeiterfassung.cloud/skillfactor/skills-core/recruitment-consultant/src/branch/main/PROVENANCE.md)
+for a fully enriched split).
+
+## Licensing
+
+This marketplace includes information from the O*NET Database (v30.3,
+USDOL/ETA, CC BY 4.0) and ESCO (v1.2.1, © European Union —
+[conditions](https://esco.ec.europa.eu/en/use-esco/download)).
+skillfactor is not endorsed by USDOL/ETA or the European Commission.