docs: Standardize documentation headings (remove multiple # H1)

- Remove multiple single top-level (# H1) headings per file
 - Use (# H2 and ###### H6) sub-headings for consistency
 - Remove any trailing # in the headings
 - This ensures proper table of contents rendering in MkDocs.

 - Also removed RUN_NR_multiple_BWPs.md as it is moved to MAC usage

doc/RRC/rrc-dev.md

@@ -8,7 +8,7 @@ separate page](./rrc-usage.md).
 
 [[_TOC_]]
 
-# General
+## General
 
 5G RRC is basically an ITTI message queue with associated handlers. It
 sequentially reads received ITTI messages and handles them through the function
@@ -26,7 +26,7 @@ possible to find the message in the switch based on a message name in the spec.
 Note that RRC is inherently single-threaded, and processes messages in a FIFO
 order.
 
-# Sequence Diagrams of UE procedures
+## Sequence Diagrams of UE procedures
 
 The following section presents a number of common UE procedures for connection
 establishment&control, bearer establishment, etc. The intention is to help
@@ -66,7 +66,7 @@ sequenceDiagram
   ue->>cucp: F1AP UL RRC Msg Transfer (RRC Message Answer)
 ```
 
-## Initial connection setup/Registration
+### Initial connection setup/Registration
 
 This sequence diagram shows the principal steps for an initial UE connection.
 This can either happen through a _Registration Request_ (e.g., UE connects
@@ -164,7 +164,7 @@ sequenceDiagram
   cucp->>amf: NGAP PDU Session Resource Setup Resp
 ```
 
-## Reestablishment
+### Reestablishment
 
 The following sequence diagram shows the principal steps during a
 reestablishment request. When handling the RRC Reestablishment Request at the
@@ -210,7 +210,7 @@ sequenceDiagram
   end
 ```
 
-## Inter-DU Handover (F1)
+### Inter-DU Handover (F1)
 
 The basic handover (HO) structure is as follows. In order to support various
 handover "message passing implementation" (F1AP, NGAP, XnAP), RRC employs
@@ -264,7 +264,7 @@ sequenceDiagram
   sdu->>cucp: F1AP UE Context Release Complete
   Note over ue,tdu: UE active on target DU
 ```
-## Inter-gNB Handover (N2)
+### Inter-gNB Handover (N2)
 
 This is an inter-NG-RAN procedure. The N2 handover specification is defined in the following documents:
 
@@ -278,7 +278,7 @@ This is an inter-NG-RAN procedure. The N2 handover specification is defined in t
   - Includes messages like Handover Request, Handover Command, and Handover Preparation.
 * 3GPP TS 38.331 (RRC): details the UE-level RRC procedures involved during handovers
 
-### End-to-end flow
+#### End-to-end flow
 
 ```mermaid
 sequenceDiagram
@@ -353,9 +353,9 @@ sequenceDiagram
   Note over ue,tdu: UE active on target DU
 ```
 
-# Structures
+## Structures
 
-## Cells
+### Cells
 
 OAI 5G RRC does not actually handle multiple cells as of now, but multiple DUs,
 each being limited to one cell.
@@ -363,12 +363,12 @@ each being limited to one cell.
 Cell-related data is stored in `nr_rrc_du_container_t`, and kept in a tree
 indexed by the SCTP association ID.
 
-## CU-UPs
+### CU-UPs
 
 CU-UP information is stored in `nr_rrc_cuup_container_t`, and kept in a tree
 indexed by the SCTP association ID.
 
-## Transactions
+### Transactions
 
 The RRC keeps track of ongoing transaction (RRC procedures) through a per-UE
 array `xids`, which is indexed with a transaction ID `xid` in `[0,3]` to keep
@@ -385,7 +385,7 @@ However, it might be possible to trigger a procedure while another is ongoing.
 As of now, no queueing mechanims exists to ensure only one operation is
 ongoing, which would likely also simplify the code.
 
-## Handover
+### Handover
 
 Handover-related data is stored in a per-UE structure of type
 `nr_handover_context_t`. It is a pointer and only set during handover