Make Stellar testnet indexer runnable locally with Bun

[0xMegie]

Summary

closes #180

• add root-level Bun scripts for indexer codegen, build, dev, and start flows
• normalize apps/s03-indexer scripts so the local path does not use npm, yarn, or pnpm
• add .env.example with Stellar testnet defaults and local standalone defaults
• update SubQuery config to read endpoint, chain ID, and Soroban endpoint from env with safe testnet defaults
• document required local services, Docker requirements, ports, env vars, and generated artifact policy

Verification

• bun install
• bun run --cwd apps/s03-indexer codegen
• bun run --cwd apps/s03-indexer build
• docker compose -f apps/s03-indexer/docker-compose.yml config

Notes

• project.yaml, dist/, and src/types/ remain generated artifacts and are intentionally ignored.
• No npm, yarn, or pnpm lockfiles were introduced.

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[IbrahimIjai]

Strong work, clean script normalization, the committed-vs-generated decision is made and documented, and the env split matches the spec. Two things before merge, then nits:

1. You've proven it builds, not that it runs (blocking). Verification stops at Docker Compose config, which only checks compose syntax — it never boots the stack. The deliverable is "runnable locally," so please run bun run indexer: dev from a clean checkout and attach evidence: docker compose ps with all three services healthy + a GraphQL playground screenshot at localhost:3000 returning data.
2. Env is baked at build time — document it. project.ts reads process.env.* during codegen/build and bakes it into project.yaml, so editing .env then running only indexer: start won't change endpoints — you must rebuild. Indexer: dev does that for you, but the README reads like these are live runtime knobs. Add a line saying endpoint/chain changes need indexer:codegen && indexer: build.
   Nits:

Add Closes #180 — the drips-wave bot flagged it's untracked; without the link, it won't count toward the Wave.
Quote CHAIN_ID in .env.example (spaces +; break direct sourcing).
.gitignore lists dist/ twice; build: develop expects an unshipped .env.develop.

#1 and #2 to merge, the rest are quick. Clean PR overall.