fix: standardize user id field to req.user.sub across routes

[Ashusf90]

Description

This PR resolves inconsistency in how user IDs are accessed across different routes.

Changes Made

• Replaced all usages of req.user.id with req.user.sub
• Ensured consistent use of JWT standard claim (sub) across:
  • users routes
  • symptoms routes
  • posts routes
  • bookings routes

Why This Change

• sub is the standard JWT claim for user identity
• Prevents potential bugs if id is not mapped in middleware
• Improves consistency and maintainability

Closes #7

[Aman-Cool]

hey @Ashusf90; Thanks for picking this up! The direction is right but there are two problems that need fixing before this can merge.

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Bug - typo introduces a regression

In posts.js, the like-toggle route has a typo:

// line ~63 — POST /:id/like
const userId = req.user.aub;   // ← should be req.user.sub

req.user.aub is undefined, so:

• (p.likes || []).includes(undefined) always returns false — the liked flag is always wrong
• The likes array gets undefined pushed into it and written back to the DB, corrupting stored data

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Incomplete - symptoms.js and bookings.js not updated

The issue listed four files with the inconsistency. This PR only touches posts.js. The following files still use req.user.id and need the same change:

• server/src/routes/symptoms.js
• server/src/routes/bookings.js

(users.js already used req.user.sub so that one is fine.)

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Once those two things are fixed this looks good to merge. Happy to re-review quickly.

[Aman-Cool]

@Ashusf90, any updates?