docs: add the DPG badge to the Rafiki footer (DOCSDEV-78)

[Infi-Knight]

Description of changes

Rafiki is now a verified digital public good. The DPGA asks projects to show the badge and to link it to their registry profile page.

The footer now carries the official badge above the existing legal text. It links to https://www.digitalpublicgoods.net/r/rafiki and reads "Rafiki is a verified digital public good."

DpgBadge.astro holds the official SVG from DPGAlliance/dpg-resources, released under CC0 1.0. The colored badge draws the letters and the check as transparent holes, so it does not read on a dark background. The dark theme fills every path white instead. That matches the official white variant of the badge, which uses the same geometry.

Melissa needs to sign off on this. Please check the footer on the deploy preview in both themes.

Closes DOCSDEV-78.

Checklist

• PR title is prefixed with docs:
• PR title includes the Linear issue ID
• You've run pnpm format and pnpm lint
• Vale does not cover .astro components, so there is nothing to review here

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[github-actions]

🚀 Performance Test Results

Test Configuration:

• VUs: 4
• Duration: 1m0s

Test Metrics:

• Requests/s: 44.56
• Iterations/s: 14.86
• Failed Requests: 0.00% (0 of 2678)

📜 Logs

> performance@1.0.0 run-tests:testenv /home/runner/work/rafiki/rafiki/test/performance
> ./scripts/run-tests.sh -e test -k -q --vus 4 --duration 1m

Cloud Nine GraphQL API is up: http://localhost:3101/graphql
Cloud Nine Wallet Address is up: http://localhost:3100/
Happy Life Bank Address is up: http://localhost:4100/
cloud-nine-wallet-test-backend already set
cloud-nine-wallet-test-auth already set
happy-life-bank-test-backend already set
happy-life-bank-test-auth already set
     data_received..................: 967 kB 16 kB/s
     data_sent......................: 2.1 MB 34 kB/s
     http_req_blocked...............: avg=7.39µs   min=2.06µs   med=5.34µs   max=1.18ms   p(90)=6.71µs   p(95)=7.49µs  
     http_req_connecting............: avg=961ns    min=0s       med=0s       max=1.11ms   p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=89.07ms  min=6.41ms   med=70.93ms  max=488.9ms  p(90)=155.28ms p(95)=185.96ms
       { expected_response:true }...: avg=89.07ms  min=6.41ms   med=70.93ms  max=488.9ms  p(90)=155.28ms p(95)=185.96ms
     http_req_failed................: 0.00%  ✓ 0         ✗ 2678
     http_req_receiving.............: avg=98.37µs  min=27.7µs   med=85.21µs  max=1.86ms   p(90)=130.07µs p(95)=176.09µs
     http_req_sending...............: avg=37.75µs  min=8.38µs   med=25.68µs  max=2.24ms   p(90)=45µs     p(95)=63.97µs 
     http_req_tls_handshaking.......: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=88.93ms  min=6.2ms    med=70.79ms  max=488.83ms p(90)=155.15ms p(95)=185.84ms
     http_reqs......................: 2678   44.556683/s
     iteration_duration.............: avg=268.91ms min=178.82ms med=251.88ms max=899.9ms  p(90)=340.88ms p(95)=371.8ms 
     iterations.....................: 893    14.857774/s
     vus............................: 4      min=4       max=4 
     vus_max........................: 4      min=4       max=4