Fix/mobility-devkit: resolve validation errors across devkit and example payloads

[riteshkparouha-cyber]

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Devkit & Infrastructure

1. Network ID corrected — changed nfh.global/testnet-mobility →
   nfh.global/testnet in devkit config to resolve failed to lookup registry:
   context.network_id "nfh.global/testnet-mobility" is not in
   network_memberships of subscriber "bpp.example.com"
2. context.try removed from sandbox payloads — stripped from all actions
   outside update and cancel in sandbox-payloads/; spec restricts try to the
   two-phase preview/commit pattern on those two actions only
3. Sandbox BPP volume path updated — changed volume directory of
   sandbox-bpp to serve static payloads through nfh.global/testnet
4. Catalog request examples removed — removed catalog-related request
   examples from docs/example_implementations/ride_hailing/; mobility discover
   is peer-to-peer so the catalog flow does not apply

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Example JSON Fixes

All fixes are grounded in the Beckn Protocol Specification v2 — beckn.yaml.

• error.details.cause type corrected across 172 files — Example payloads
  were using a plain string (e.g. "cause": "downstream timeout") as a
  placeholder for this field. The spec defines cause as a self-referencing
  Error object, enabling structured, typed error chains (e.g. wrapping a
  registry failure or provider error inside a parent error). A string value
  fails schema validation and loses that chain structure entirely.
• context.try removed from 117 non-update/cancel payloads — The try flag
  enables a two-phase preview/commit pattern where the receiving NP computes
  revised terms without mutating state. The spec only defines this behaviour
  for /update and /cancel. Including try on actions like discover, init,
  confirm, etc. is meaningless per the spec and was carried over as
  copy-paste noise from update/cancel templates.
• quantity added to commitments[].resources[] in 14 files — The spec marks
  quantity as a required field on every resource item inside a commitment
  (alongside id). It was missing from the generic lifecycle example files,
  causing schema validation to fail on those payloads. Added as {"value": 1,
  "unit": "unit"} to satisfy the constraint.
• GeoJSONGeometry.bbox corrected across 18 files — The spec enforces
  minItems: 4 on bbox, representing a bounding box as [west, south, east,
  north] (southwest lon/lat + northeast lon/lat) per the GeoJSON standard.
  The placeholder value [0] was a single-element array that both violates the
  schema constraint and carries no geographic meaning.